Looking for source for large slate frame or alternative for Starmore's Spiral Chessboard

Anyone have a source for large slate frames?
I've not used a slate frame before but would like to give a try on a
couple of large patterns from Alice Starmores Celtic Needlepoint; Key
Pattern Cushion 25inch by 25inch and perhaps Spiral Chessboard
30inches by 30 inches.

On the web Viking sells a slate frame 27 by 18
Leon Conrad sells frames 27 by 27 large enough for the Key Pattern but
not for the chessboard (unless I've miscalculated somehow)

Alternately, those of you who have worked on the Spiral Chessboard,
what frame did you use and what were the advantages and disadvantages?

Yes, I'd love to ask my guild or local needwork store but I live way
out in the boonies and no such critters ‘round here. I do my shopping
on the web.

Thanks
Shelley

i was going to suggest viking. I got my slates from them... haven't put the
piece in 'em.. now it's almost done. Eh well, next big piece will surely go in
the slate frame!