Once a year Ilford invites orders to manufacture film in a number of non-standard or obsolete sheet film sizes. It's known as the ULF film order, but it isn't restricted to ultra-large format film. Although it is possible to cut smaller sizes of sheet film from 4x5 or 10x8, it's a great advantage not to have to do this oneself for a number of reasons. I've got a box of HP5 Plus in 9x12cm format, to use with my Recomar and Avus cameras, which must have been produced from the ULF order (although I didn't specifically place the order for the film size myself).
Of the sizes Ilford are proposing to supply this year, the announcement of HP5 Plus in 50ft lengths of 46mm, the size of 127 format, has caused a little excitement: since Fotokemika stopped production last year, there has been a niche, admittedly small, to be filled in the roll film market. Obviously this does still mean rolling lengths of the film with 127 backing paper, but it removes the need to slit medium format film down to size.
The deadline for orders this year is Friday 28th June. For more information see Ilford's website: http://www.ilfordphoto.com/products/page.asp?n=137