Ace Miatas and More in Lewisville or Track Dog Racing in Dallas/Garland are the two best options. If you need to keep it on a really tight budget, you might try to track down Jerome (JDSM) or Mitchell Palmer, as they do a lot of side jobs.
What is the symptom that makes tyou think it is the TO bearing? The pilot bearings are notorious for failing on miatas as well, along with clutch/slave issues.