How do I buy doors of non-standard size?

[WalkingThePlank]

I have to replace 2 internal doors of the following sizes:

1817 x 602mm
1818 x 588mm

We want either white doors or wood that we can paint. The height of these is the tricky bit. How do I go about buying such doors without spending an eye watering amount?

I would suggest either trying a reclaimation yard, or choose a 72" x 24" (solid not pressed) door and plane to size.

Ebay or a local reclamation yard

I got some at a local antique furniture shop. I asked the chap who owned the shop where I could get some (don't know the area well) and by luck he had an old storage shed full of lovely old doors of all shapes and sizes that he didn't know what to do with. They were very reasonably priced too (cheaper than ebay).