I know about this website (Wixey).. however on CNC forum someone mentioned they (or the new rep in Canada) are a bit slow in responding to small quantity enquires..
(see here)
The reading head is designed for linear movement measurements (the strip must be flat where the reading head is) but perhaps the small curvature of the strip can be tolerated
However, U$35 (plus US29.99 for head) is not such a big loss in exchange for potentially excellent encoder (I can already see the direct application on small lathe or milling machine.. or focuser).
Attached are the dimensions of the strip (taken from before mentioned CNC forum)
Some Chinese suppliers may offer even a fraction of the above price for all this (Chinese calipers are using different data format at output port, it is not Digimatic standard protocol...
It is documented
here and
here )