Hi Dave,
I'm sure Mike Boxall at the site Sponsors could help you with suitable descaling products that won't affect the Stainless Steel.
I'm just going to try a product range that works using Bacterial & Enzyme cleaning agents which apparently help in keeping the whole toilet system clean & safe.
The Blurb looked good, but as the saying goes "the proof of the pudding is in the eating"....or maybe not in this case
Les