Glideslope panels (see AIM 2-1-2-e, "Alignment of Elements Systems") are even rarer than tri-color VASI. Cheapness is the big advantage, but they're only usable on short final (3/4 mile.) Here ya go:
1N5 Bennett
2W2 Clearview Airpark
D49 Columbus Municipal
E05 Hatch Municipal
FRR...