The post card rate is 32 cents now so you don't want any 29 cent stamps at all. There's a chance the postal services could return them to sender for additional postage. There are currently no other stamps at the post office except the 32 cent Aloha stamps.
However, 32 cents use to be the first class rate at one time and you can find mint sheets of 32 cents stamps online at sites like
ebay all the time. There is Scott #2968 Texas statehood stamp which has a rider on horseback and Texan flag - western like. There's the Civil War sheet, Scott #2975 which is at least around the same time period. American Indian Dances, Scott 2072-3076 could work into your theme as well. Scott 3220, Settlement of the Southwest has a Spanish Mission. Any of these can be found on
ebay at face value or close to it if you look around enough.
Now, if you are willing to put a 29 cent stamp along with a 3 cent stamp, there's the Legends of the West sheet, Scott 2869 which would be perfect. the 3 cent stamps can be had at the post office - usually the 3 cent star or the teapot. You might have to pay a bit more than face as it's popular and avoid the recalled version Scott 2870 as you don't want to use that for postage and it sells for a lot more.
Also to note, the majority of these 29 and 32 cent stamps are from the 1990's and are the lick and stick style, before self-adhesive stamps.
Hope that helps,
Will