Fairly easy to get hold of thanks to a big find about 18 months ago (saw the market drop form £60 a pair to £25 a pair), however drying up again now. A pair of 1.75's go for around £25 - £35 posted - but I'd say these will go up soon.
2.125" are very rare however - not seen any NOS for over 3 years. But there have been a few used around.