The NHS have given out a number of SpaceOAR to a set of hospitals to try out. This was a couple of months ago, and they were supposed to be used in as many different scenarios as possible. You might find some hospitals with some of these free ones left.
I was considered for one of these, but in the end, it was decided I'm not a good candidate for SpaceOAR (NHS or private). I had been intending to do it privately, but they said if I had been suitable, they would have done on the NHS using these trial ones they were given.
I suspect it will become standard on the NHS for suitable cases.
One of the things that made it unsuitable for me is I'm classed as high risk.
High risk is PSA >= 20, or T3 or above, or Gleason 8 or above.
The reason for this is the theoretical risk of pushing micro-mets away from the X-ray field by the spacer is currently considered too high to justify its use.