Need 12m transwell inserts for 12 well plates (or 24wp)

It seems as though Corning Costar have suspended manufacturing their 12m tissue culture inserts (Transwells).

I've tried out 8m inserts from BD Falcon and Greiner but both had problems to do with cell seeding once the inserts had been collagen coated. The BD inserts didn't seem to bind collagen very well whilst the Greiner inserts actually allowed a second monolayer of endothelial cells to form on the lower side of the insert (which might be interesting for some people's work but not mine).

Any suggestions for sources of alternatives would be very welcome.

Thanks