I've purchased recently two fool-proof guaranteed working Tualatin motherboards on eBay, specifically two brand new in box ECS P6S5AT that I can use even with DDR memory.
I haven't received them yet, and was wondering if it was feasible that they support more than 1 GB memory. In any case, they seem to pop up quite frequently on German sellers according to "finished items" search.
I never had any luck with slockets. The last PIII I've left to test with is an IBM PC 300PL one, which supported FSB 133 MHz. on slot 1, even if I don't know if it includes the necessary VRM. Never managed to grab one of those expensive slotckets that came with their own VRM, although I did see one working on an old motherboard and a Celeron Tualatin.
I have, however, a healthy quantity of P3 Tualatin 1.4 GHz. SMP CPUs that I would like to put into some use, so I decided to buy a couple of boards and have them doing something; even basic word processing. My memories of Tualatin processors are that they were CPUs from another planet: putting a 933 MHz. Coppermine besides them was almost an insult and my very expensive but useless Pentium 4 1.7 GHz. with Rambus wasn't able to cope with tasks as efficently as the Tualatins.