Nobody answered so ...........................
This isn't a recommendation, but you need either an i820 or i840 mobo to use a slot 1 CPU with RDRAM. Hopefully you're only considering this because you have access to some free RDRAM, because it isn't worth buying.
That being said, the Intel VC820 is available starting at about $35. Some others are available on Pricewatch from Transcend, Acer, and Gigabyte for considerably more cash. Dunno much about them though.
The i840 chipset is used in expensive dual CPU mobos and there are also some pricey i820 dual CPU mobos also.