I want to know if there's a published prestige class where I can get martial maneuvers and stances as well as divine spells.
Ruby knight vindicator on Tome of Battle page 122 can be entered by a 4th-level paladin/1st-level crusader and will do exactly what you are looking for. It is, in fact, the only class that will. At 7th level, it gets the fantastic divine impetus ability, which allows you to use turn undead uses to gain extra swift actions.
Please note the Battle Blessing feat from Complete Champion, which makes all paladin spells a swift action. This is excellent for all paladins, but for paladin-based ruby knight vindicators it becomes absolutely amazing.
In addition, either the Dynamic Priest feat from Legends of the Twins or the Serenity feat from Dragon Compendium is highly recommended for any paladin that cares about his spellcasting, as they reduce the multiple-ability-dependence of the class. Dynamic Priest allows you to ignore Wisdom as your bonus spells become Charisma-based, while Serenity allows you to ignore Charisma as all your paladin class features become Wisdom-based. That means you can focus more on one or the other and have more uses of turn undead and more spells.
Also note that ruby knight vindicator, as written, requires you to worship Wee Jas. Normally, paladins don’t actually have strict requirements about their faith—you could argue that praying to an evil god is an evil act and thus against their code, but there is no explicit rule about it and otherwise you’re definitely okay. The Forgotten Realms has stricter rules, but Wee Jas is from Greyhawk anyway, and even in FR, an LN deity can sponsor LG paladins (Forgotten Realms Campaign Setting suggests Azuth or Kelemvor as stand-ins for Wee Jas; both are LN and explicitly have orders of paladins—Kelemvor’s even get a special name, the Doomguides). But if for you do not wish to worship Wee Jas, Tome of Battle also includes this note:
Although this prestige class is specific to a single crusader order—the Ruby Knights of Wee Jas—you could easily adapt it to crusaders devoted to almost any other deity.
Notably, the example “ruby knight” vindicator in the book actually worships St. Cuthbert.
Finally, there is an existing answer with discussion of various options for a paladin-based ruby knight vindicator, which may be useful. It focuses somewhat on healing specifically, but many of the techniques there will apply however you want to use your spells.