I doubt if you will find anywhere to get exchange UK bottles, the only exception is Camping Gaz which can work out expensive. Your options are to buy a bottle & regulator in which ever country you are in or go for a refillable system. Refilling bottles is easy throughout most of Europe but you will need 4 adapters to cover all of Europe. You can manage with one refillable bottle & also carry your Flo Gas bottle as a back up in case you run out, you can use it until you refill the refillable bottle.
Alternative method you can buy an adaptor of ebay to fill your Flo Gas bottles BUT you must take care to only fill up to 80%, this is done by knowing the weight of the bottle empty & the weight of gas you will put in, failure to know you aren't overfilling can be highly dangerous.
Many years ago I used to get by for 3 weeks in my old Kontiki with 2 x 6kg bottles (used to carry an extra one under one of the seat lockers but never needed it).