Can't you buy a can of 134A or whatever the fridge unit specifies on t'internet and do it yourself?
I've got a £15 1Kg can that's done a couple of boat refills and one on the car and still isn't half empty. It isn't rocket science.
Has your fridge a charging point, and have you discovered where the gas has leaked ? If it isn't sealed it will leak again. Just topping up may not resolve the problem. If this is a two part system then it should be evacuated first. You may get away with charging, venting off, then re-charging, but this is not a proper way to charge a fridge system. Be aware venting refrigerant and charging a leaking system are both illegal actions.