I wish we had a picture of the carbine put together, but it looks like you have a very nice original WW2 high wood that was never rebuilt. If it is indeed an original never refurbished Underwood, here in the states that would be worth somewhere around $2-3k minimum, possibly a lot moreFrom the looks of it it has the wide front barrel ban sans bayonet lug, which would be correct for an original 1943. Plus nice cartouches. And Underwood was the third largest manufacturer, incidentally the third to get production up and running after Winchester and Inland, but they only made 545,000 carbines compared to 800+k by Win and 2.6m+ by Inland, so they are far less common than the other 2. But even the other two if original unrestored can bring that much so I may be low.
Most carbines have been rebuilt many times so the parts do NOT match, and even those are getting up there, $800+ In otherwise good shape.
Now a lot of these were given to the Free French and I believe the French Army used them after the War for some time, and if it was used by the French and possibly rebuilt by French Arsenals that could negatively affect the value, but if it is a US issue somebody had stored away since WW2 and it’s untouched it would be very highly sought after by collectors here.
I have no idea what the controls or laws are over there, but I know there are collectors with deep pockets in Europe, and if you could get the word out you might find a rich US collector or auction house who would jump through the hoops to import it and maybe even sell it for you on consignment, and they’d deduct their expenses and fees, IF it is an unaltered original...