I would contact SME directly. I did when in the same situation a few years back, the screw was expensive about $ 50 or so when all postage etc was figured in.
Yup, I ordered one thru a local dealer and got it within a few weeks. You can set the VTA without it. Just loosen the clamp screws and you can move the arm up and down by hand, Just like many other arms. It would work to get you started if you want to set it up before getting the part. BTW, I'd buy an extra allen wrench from them that adjusts the height of the armrest. It is a weird "Witworth" size you can't get just anywhere. I misplace mine and couldn't get the armrest out of the way for a couple of weeks!
Thank you for that info, never have heard of the BSW thread pattern. Seems like the SME VTA Screw is 1/8" BSW, looked for Screws which seem very hard to find especially in the length required, However a Die can be bought for GBP 5 http://www.tapdie.com/html/bsw-_dies.html
so one could easily make one from a piece of Stainless Rod or similar.
Done a little more research the thread size is 6BA
Correlates with the apx 2.7mm thickness and the 48 threads per inch
Found some all thread on eBay but the seller in England will not ship to the US
Don't know if above will ship to the US but it might be worth a try
Best of Luck