My online supplier (paddockwood here in Canada) isn't carrying biscuit malt anymore either. I'm very interested in a close substitute. I haven't tried it yet as a direct substitute but victory malt also has biscuit notes to it.
The special roast that b3 sells is a biscuit malt. 50L. I've used it a bunch in english bitters. It's kind of more subtle than a full on biscuit malt from what I can tell.