i still have a pair of GEC 6080WA
http://www.ebay.com/itm/321312637695?ssPageName=STRK:MESELX:IT&_trksid=p3984.m1555.l2649
GEC 6AS7G are found on ebay, those uk sellers, they can be pricy though, curved base pair for like 572$ and single straight bases for 200+ and 250 + for curved. they tend to sell singles more than pairs too.
i got 1 gec single left as well. i sold all my curved/straight pairs. so hard to find... seems like those UK sellers on ebay really control the market, i rarely see anyone else put any up for sale.
soundwise, i think GEC 6080WA are really nice, warm and less airy than 6AS7G instead of being open and airy, they tend to be warmer and more bodied almost like a tung sol but different, almost RCA like in some ways, but without that crappy treble those have.