As the title implies, I'm wondering if there is any way for a Warlock of the Fiend to learn the spell Blink preferably without multiclassing. I have some plans with the spell but as far as I have been able to find there's no way for me to get the blink spell as a warlock without either multiclassing into another class that can learn it and leveling until I get a third level spell slot in that class or having my patron be either the Hexblade or the Archfey.
The only way for the warlock alone is through True Polymorph (possibly)
The only way for a warlock to gain access to the blink spell is through a 9th level Mystic Arcanum of true polymorph. You can use that spell to turn into a monster that has access to the blink spell innately. As of writing this, there is no official monster who can do this.
You can try a Voyager Staff
There is one magic item, found in Guildmaster's Guide to Ravnica that grants access to the blink spell. It is called the Voyager Staff, and as long as you never expend the last charge, you don't run the risk of losing access to blink.
If you expend the last charge, roll a d20. On a 1, the staff vanishes forever.
A Ring of Spell Storing provides a refillable option1
Another magic item that could work is the Ring of Spell Storing which lets another spellcaster provide you with access:
Any creature can cast a spell of 1st through 5th level into the ring by touching the ring as the spell is cast. The spell has no effect, other than to be stored in the ring.
Granted, you could only store one casting of blink at a time, but if you have a friend with the spell, this would work long term.
1: Credit to medix2