It seems like most, if not all, early 90s GT MTBs were All-Terra. If it's in good shape and it's a Karakoram that's a pretty good deal. If it's an Outpost, not as good a deal.

If it has a one inch headset you'd have to cruise eBay for forks and I'm not sure how many 1" steerer suspension forks with disc tabs are out there.