My home range is in a tunnel with trees on both sides, with the result that the target does not get any light until late morning or afternoon, making it difficult to spot hits, especially with rimfire. I started placing 6" Shoot-N-See targets over the bullseye, which fit perfectly over the 22 ring, which made a big difference. Then I realized that with a black marker and a compass I could easily re-draw the scoring rings to match up with the standard Schuetzen scoring rings. The inner ring on the shoot and see is only slighly larger than our 25 ring so I leave it alone. Then using a compass, I scratch out two rings marking the 23 ring,blacking out the rings that we dont need. I could not resist adding the "23" and "25" numbers, which obviously are not necessary.  Now I can practice in the early morning, before the heat sets in and avoid the heat of the early afternoon and  late afternoon when the mosquitos take over. 
I hope this helps those who are in a similar situation. 
Joe S

I found that I could get 60 six inch targets at Amazon for about $16 which is cheap enough even for me 
Joe S