I was on the hunt for these the other week. I usually end up hacksawing the splined ones as well, but could do with some solid shaft ones as well. Haven't found any yet but have a couple more places to check - I'll report back if I find anything. Frustratingly, I have a few lying around and can't remember where I bought them. I'm pretty sure it wasn't Maplins, I hope not anyway... I hate that place and will only go there in an emergency!
Incidentally, I tried to get Rapid to stock the better JPR's better push button switches from that other thread. They sent me a sample of one alternative, but it wasn't much better than the ones they already do, and they called the search off after that. Was worth a go though - maybe they'd have better luck sourcing some of these?