eBay Belgium & eBay France appear to use the same servers and draw from the same set of listings – the only search result differences are when searching by location and looking for local items. I’ve therefore put them on the same results page.
Please note that S-gauge is a difficult scale to perform precise searches for, on French-language eBay sites.
There seems to be a French-language peculiarity where the apostrophe-S used in English to denote personal ownership (e.g. “my mum’s hat”) is used for plurals (in English, plurals don’t have the apostrophe). This causes the “s” to be standalone in search logic, and thus returns results in the same way as the “S-” of “S-gauge” (eBay search is also case insensitive, therefore using a capital “S” does not fix this).
As a result of this peculiarity, please carefully check item titles and descriptions do actually refer to S-Gauge, and have not been returned due to some other form of orphan “S”.