I spoke to SASS thius afternoon about getting a smock made in L34 ventile. They won't work in Ventile as it is a right git to work with and would involve adjusting the machines too much for an individual item, so they won't do it. Maybe for a bulk purchase, but it would have to be a few. So I asked about the material they use. They made some in ventile years ago, but won't really do it again. Instead, they use the military spec treated cotton. This is water resistant. Not 100% waterproof, but it does swell when wet, but initially the water just beads and runs off. My current DPM smock is the same stuff and it's quite impressive. The MOD rates it just under ventile for breathability, toughness and proofness. Therefore, after much debate I have opted for their fabric, and will order a smock in OG and matching Soldier 95 pattern trousers in the same material. All in for about £155. Not bad methinks. I'm awaiting a sample of the fabric in the post before confirming the order. I am also ordering the standard size Rhoesian belt puch in OG with clips which takes two '58 bottles. I am thinking it will be ideal to carry the ubiquitous Swedish Mess Kit Trangia set. The pouch has clips on it to either mount on a PLCE type belt, or a shoulder strap can be attached via more clips that are built in.
So to summarise, if you want a custom bespoke smock in ventile, then this one of Garrys is probably your only choice! And a nice one it looks too.