It may be worth taking a look at what Kempton has to offer next Sunday - I found a Club Mark 2 at the last one.
I have Target Mercury and swapped the standard 1.1 mm eyepiece for an adjustable one. It made all the difference and now the rifle is as accurate to use as a Webley Supertarget or similar.
Good luck in finding an aperture sighted Airsporter/Club - you won't regret it!
John