I have bought a range of materials from Horbarts in the UK but I haven’t got a Glowforge to test them with yet! I actually bought them years ago when I was planning to build my own laser cutter but never got around to it. I have 1W and 12W near IR diode lasers, so I might actually put together a laser cutter before my Glowforge arrives if it doesn’t come this summer.
Laser diodes give a much smaller spot than CO2 so you don’t need as much power to get the same power density. They are only just below the visible spectrum though, so you can only cut optically opaque materials that don’t reflect red light.