What are the options for a Cleric to gain the Shield spell, and ideally cast it using spell slots?

Question

I am looking to build a order domain cleric, and looking at ways to obtain the shield spell. Specifically I hope I can learn it in a manner that allows me to spend my spell slots on it.

So far I have found the following:

1. Multiclass - This is the only method I have found that meets my main criteria, but has a host of downsides
2. Magic initiate - Apparently I can't use my spell slots so this is 1/day only. See: Can you cast a spell learned from the Magic Initiate feat using spell slots?
3. Aberrant dragonmark - Counts as a sorcerer spell so I still can't use my spell slots on it (probably)
4. Talk to my DM - Unlikely to work because he knows I am a bit of a powergamer (hence wanting the shield spell on top of heavy armour, a standard shield and probably a shield of faith spell too)
5. Cheat - Just hope my DM doesn't notice it isn't a cleric spell or doesn't know the rules around class spells and spell slots - not my style
6. Get a magic item (I am not sure there even are any) - this isn't really an option even if one does exist, because the DM rolls for loot

I can use all legal source books, but have I misinterpreted anything I have above, or missed any options?

Bonus points if someone can find a way that also gets me booming blade :)

Answer 1

The options you've found are described correctly

Multiclassing, taking the Magic Initiate feat, talking to your GM, cheating, and getting a magic item all function exactly as you've described.

The strange one there is the Aberrant Dragonmark which cannot be cast using spell slots unless you are a Sorcerer. This would be similar to Magic Initiate in that you cannot use spell slots on a spell that is not associated with your class(es). The feat also does not make an explicit exception like some others do. For example, the Artificer Initiate feat:

[...] You can cast this feat's 1st-level spell without a spell slot, and you must finish a long rest before you can cast it in this way again. You can also cast the spell using any spell slots you have. [...]

Lacking similar text, I would conclude that without multiclassing into Sorcerer at least one level, you cannot cast the shield spell granted by the Aberrant Dragonmark with spell slots.

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There are few other options, none of which work

The other ways to be able to cast shield at all do not allow you to cast it with spell slots. These methods are being a Githzerai from Mordenkainen's Tome of Foes and being a Mark of Sentinel human from Eberron Rising from the Last War. Both of these only grant the spell once per long rest though, and neither add the spell to your spellcasting list nor explicitly state that you can cast it using spell slots,

Answer 2

(Note: answer based on first version of the question.)

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Since you use heavy armor, STR can't be your dump stat. Therefore you could take 3 levels of fighter to become an Eldritch Knight. INT is irrelevant then, and to offset losing 3 levels of cleric and some spell slots, you get a fighting style, Second Wind, 1 Action Surge, 2 cantrips and 3 1st level spells, including option to take Shield and Booming blade.

As for role play justification to multi-class, you're already wearing heavy armor, seems like you want to fight, so wanting to become extra good at it seems fitting.

Starting with fighter would also give you weapon and armor proficiencies, potentially opening more Cleric subclasses for your consideration for same character concept. Remember that classes are an abstract mechanical concept, and don't really exist in the game world. You can easily be a warrior priest even if your 1st class is mechanically fighter.

Answer 3

The Ring of Spell Storing, and another caster with the Shield spell

According to answers in this question, you can cast a reaction spell into the Ring of Spell Storing. This works through teamwork, but even then you can probably only do it 5 times before you need to refill the ring. Here's how to do it:

1. Acquire the Ring of Spell Storing
2. Befriend or pay someone who knows the Shield spell
3. Attack them, ideally without them taking too much damage
4. Have them cast Shield into the ring
5. Repeat five times
6. Have them give you the ring

Since your DM rolls for loot, this method might be out of your reach unless you can find one outside of loot. Best of luck.