Half-inch, full-track master? I assume that's in stereo?
Man, that's such a specialized thing now, that it may be kinda hard to find any pro studio that still has that format. Hard, but hopefully not impossible.
JFYI, if you want to go the Ebay route, I saw a Fostex E22, 1/2", full-track/stereo R-R, and it was reasonably priced, [can't remember exactly],... maybe $350. IMO, 1/2" 2-track are generally hard to find.
Sure, you requested info on services, and not necessarily hardware. You may not want to spend hundreds of dollars on unknown used hardware, if you just have one reel you want to transcribe.
Well, I can't help you on a services lead, and I really can't help you on hardware either, except to point you to Ebay.
Sorry, I guess this post is of no help,... but good luck on your search! Wish I could help more!
