The NT30 taper is quite a bit bigger than the R8 so any adapter would put the cutter a long way from the end of the quill and not be ideal for rigidity.
It's not a problem. The change over to R8 tooling hasn't been too expensive (probably about $500 to get set up again). R8 prices are pretty good as it's common. I just picked up 3x new R8 ER40 collet chucks on eBay for $160 delivered. Quality seems pretty good too.
Cheers