If you don't need a boxed example, then there are plenty of Juniors available either through here or at arms fairs that can be had from about £60-£80 in good shootable condition. I have 5 ( don't ask! ) and bought the last one last october at an arms fair for £70 and it's a nice little shooter as well as being desirable.
Stay away from the tin grip/early ones unless buying purely as a collectable. In my opinion, the models from the 50'-60's era are the nicest and the later mk11 junior/plastic coated, out of character for your Service rifle.
All juniors were .177, Premiers in both .177 and .22.
Premiers tend to fetch a bit more but might not suit, depending on arm strength etc.
Search 'collectables' for both and you should find quite a few recent items offered. No idea if any are still available though.
Hope this helps
Carl.