From what I have read recently on other well known large forums, locating refill stations is becoming more difficult. BP & Shell seem to be removing them when they refurbish and other locations just seem to discontinue.
Reports suggest for those that travel overseas ( which is a main factor for fitting them), that while outlets are closing there are still enough not to be a real problem- yet.
A developing problem in the uk for the ever growing camper van sector, though, as many only provide an under slung tank and no space left inside for exchange bottles.
Fred