It all depends on how bad it it. You could try another 75W-90 synthetic gear oil and see if it improves. It's worth running some less expensive stuff through it first anyway to clear out more debris.
Looking for local suppliers of Redline you should check race and performance shops. One of the big chains does carry it but their smaller locations still have to order it, it's more expensive and I can't remember who...
EDIT: CarQuest, PepBoys, O'Reilly, AutoZone, Advanced.... may be special order at some, but they're all dealers. Locally one or two of them actually stocks it though. I buy through a local performance shop (not a Honduh preformenz shop...).