I believe the P@H juinor pellets are made by Burgess and similar to their Excel junior pellets - what is the fibre/protein etc content as listed on the back?
If they are on a pelleted food with high fibre already then swapping to SS may not be necessary. If you are on a mixed food then you will need to swap.
Mine have been on Burgess Excel junior and are now on the normal, they seem to be doing fine on it and I can't get hold of SS easily either. Excel is available from P@H and I can get it in large bags, which is perfect for the number of rabbits I have to feed. If you find once you have the balence of pellets to hay sorted out and they still get too may soft poos then SS is supposed to be better then Excel for that problem.
but with burgress cas in a bunny thats is showing signs of a delicate belly burgress is often to rich, thats why i suguested the ss. it maybe a good idea to see if you can get allen and page id your finding it hard to get hold of the ss!
Eve x