Yes, I also used PM, very good prices however I bought 10 10mm top caps from them some time ago, but they don't fit. They're 10mm just, but don't fit 3/8" top caps. They are not the smaller ones sent by mistake either, they're too big for an EF37A, hence my predicament.
Yes, the weird "valve triangle" around Billinghurst is odd and intrigueing, that aside Langrex show non in stock on their website. As they, Billinghurst et al get these from the same place, IE China everyone's in the same boat due to the extensive Covid lockdown's that were previously in place, hence the price increases & shortages.
If these were in an enclosed transmitter or amp with 500v HTI'd go DIY but as these will be going on an amp & I'll probably sell it at some point, I can't go the DIY route.
Thanks for all your IP, some cracking idea's there I'll log away for future use, Andy.