you might want to call around to a few local tire shops and ask, unfortunately there are alot of shady places that will try to sell you a whole set all the time ive personally not heard of "within 1 in of tread wall" ive heard not to on the wall itself.
you mean they are 4/32 from new or thats what they have left? i would say you could buy one (if you can get the same brand, model, and size) if you only have 4/32 gone but if you have 4/32 left then buy 4.
1998 Bonneville SSE
2007 Monte Carlo LT-KYB, Clarion, Polk audio, Kicker
1999 Yukon SLE-KYB, Air lift, Reese dual-cam, Tekonsha
1987 Firebird-355/th400-nothing stock