The really nice williams diopter is practically unobtainable in the UK. After quite a bit of faffing around with trying to get the nice williams, being very disappointed with the williams I could get, and trying a couple of cheap diopters, in the end the best solution was to wait for a couple of 2nd hand anschutz diopters to turn up at reasonable prices. That's now what lives on my HW30S and Crosman bell target rifle.

As for foresight, I fitted an Airarms adaptor and front tunnel sight to the 30S, and fitted the fibreoptic 30S sight to a hand filed dovetail on the Crosman.