I don’t know if this helps, but I have the 18″ BBS LM wheels on my GTS. I called BBS and bought new valve stems directly from them. These wheels use a metal screw on type stem. Being they made the ACR BBS wheels I would think you could get them as well.
Those look longer than the stock ones. Also looks to be sold out if those are the right ones. I got a lot of time to track some down now (unless my old ones leak). I will try giving them a call. The websites could be wrong.
The valve stem gaskets are old and need replaced since. My tire place is having a hard time finding them. Are they some special size? Does someone have a source on where to find replacements?