Your best local place to find sheet music:
https://www.edmondmusicinc.com/
A good store to check first if looking for a new horn:
https://www.larsenmusicokc.com/
Helpful resources on horn technique, equipment, and maintenance:
https://www.engelbert-schmid-horns.com/index.php/en/
A great video to watch before you buy a new horn: