Anyone know of any? I've spent what seems like hours Googling and come up with pretty much nothing. So if anyone could point me in the right direction it'd be much appreciated.
Are you after a regular supply or just a one-off purchase? If it's the latter, you regularly see people listing blocks of spalted or flamed wood in the guitar section of eBay.

No idea where you'd look for a regular supply though.
Gibson LP Traditional, LP GT, LP Studio, SG Standard x2
Barber Tone Press > EHX Worm >TC Polytune > MXR Custom Badass 78 > EXH Glove > EHX East River Drive > Zoom G3 > TC Spark Mini Booster
Laney VC30
Marshall TSL602
Jet City JCA22H
My SoundCloud
Cheers, Gary. Only after a one-off for now. I did have a look at eBay but didn't see anything much. I will keep an eye on it though, if stuff turns up occasionally.