For INTernational transport/fares, stations do not normally apply, nor mostly companies, but so-called Border tariff-points. INTernatioal-SCIC fares are simply added up per country traversed. You canNOT buy that at any BE-station, as it must have a special INTernational ticketwindow and only the larger ones have that (comparable to BR just still a few years back).
BUT this wont be cheap, as there is also a 7 eur handling fee to be coughed up. Thats for normal tix, I DK about FIP and all that. Online there is no fee.
To please the local passenger, there are thus cheaper and no-extra-fee tickets fro the area ONLY sold at the normal windows in the area (and possible via local machines), search for ''trampoline''. Its however a lot cheaper to bus it over border and change into tram or metro from Transpole, f.e. there is the MRT bus Mouscron-Roubaix. on ALl transpole tickets you also have to pay an extra 20 or 30 cents to get that chipped card-its re-usable. And again-do NOT forget to validate=touch in!
Its also a short walk from Komen/Comines to same-named FR side, with frequent direct bus to Lille or maybe still the odd peak-hour train?