We need a board with the following:
1 x mini-PCI
1 x mini-PCIe
2 x LAN

Unfortunately, the only board fitting this description is the massively expensive RB800

BUT, a normal RB433 and RB21 combo can provide this solution at a fraction of the price!

However, I can't find a RB21 anywhere... do MikroTik even still produce them?
All I can find is this newsletter in 2007: http://www.i4wifi.cz/inc/_doc/Pdf/Mikro ... _no003.pdf

Edit:
The only real reason for needing a mini-PCIe is for adding 3G support to the router.
Can I however do this using USB? (like the RB433UAH), the technical guys at Miro (our supplier) says you can only use USB & 3G on MikroTik RB's as failover internet connections... is this true? Doesn't it add a normal interface like any other?

Hi, not true. Use usb for 3g ; )

No, you can use it for failover (makes more sense) but nothing stops you using it as the main connection. It will just show up as a modem. In RouterOS you can configure anything you want, there are no limitations like that.

Thank you for confirming that!

Still curious, why can't I source RB21's anywhere?
Do they exist?

Its very old..

This product was never produced due to a design problem - the 3G miniPCIe cards need a SIM card slot, RB21 didn't have a SIM slot, so this product was essentially useless. At the time we hoped that new miniPCIe 3G cards will have the SIM built-in, but it didn't happen that way. They all need external SIM slot, like on this device:

http://www.routerboard.com/index.php?showProduct=96