THK linear bearing rails

I am (slowly) planning to build a CNC router, and I have just got lucky and sourced some THK HRW 27 linear bearings, on a rail, and also some SSR20 s on four other rails. I think that it would be preferable to use the HRW27 s, as they are bigger and 'four way' load bearing, as I understand it. However, I only have one rail for them.

Anyone know where I can get some other rails from (and how much it would cost)? I think, if I am going to use them, I'll need one rail of 1360 long (for the other X axis), either one or two about 750 long for the y axis, and one about 200mm long for the Z.

Alternatively, I could maybe use the SSR20 s for the Y axis. Any ideas/opinions anyone?

Cheers,

Tony