Many people have been waiting weeks now to source their patio gas bottles and, having spoken with Calor, the situation doesn't seem likely to improve in the near future. For those looking for their first bottle the wait may be even longer.
There is a lot of information available on the internet regarding the use of butane as BBQ gas so this may be something to read up on. If you use a phrase such as "butane for bbq" in your search engine there is plenty of information.
Of course, it must be your decision whether to use Butane and you will need to check your appliance is suitable for butane and that by making any changes to the regulator and gas you are not invalidating any product guarantee or warranty.