gas bottle refill

Garden centres frequently have LPG, or try "Yellow pages". However, most unlikely the connection will be the same, so you will most likely need a new cylinder and a regulator. The cylinder may not even be approved for use in Belgium and thus not able to be filled legally
If you are not happy about changing a regulator and checking the system, get someone who knows what they are doing. Finally, avoid transporting LPG in a car as if there is a leak from the valve results can be disastrous, get it delivered.
Sorry to sound "a jobs worth", but decades in the industry has taught me how to keep in one piece!!