RS sell some cheap filters for their rebranded Pro'sKit SS-331H station and the cleaning rods are very good too (much better than Hakko's version). The filters are slightly larger than the ones used on my 474 station though.
CDJump on the KLOV forums came up with a great solution, using a metal hollow punch meant for leather and a ceramic paper blanket from china (ebay) to cut his own.
I got two hollow punches to cut down the RS filters, this worked great for the 3mm x 16mm filters used in the station. The filters used in the gun should really be more like 5/6mm thick though. Also the blanket has since sold out so I went looking for something else.
I found some 3mm and 5mm ceramic paper sheets (A4 size) on ebay which are perfect. A search for ceramic gasket should bring up something similar.
From a single sheet I was able to make over 200 filters.
Considering 10 filters from Hakko are £10.75 + £7.50 postage and a sheet that made over 200 was £4.99 including postage, it was quite a saving.
The hollow punches can also be picked up from ebay for about £5 each.
16mm x 3mm (not 15mm as stated on their web site)
17mm x 5mm (or 6mm, if you can find it).