Is it a physiotherapist you specifically want, or is a sports massage/ therapy suitable for what you are after. - apols if its the former.
I highly recommend Ali sizmur sports therapist if you are around okehampton (not sure how far she travels). She has tweaked numerous horses for myself & friends, really improve some on going issues & the horses all seem to love her (just be warned she has an almost over critical eye & just about every horse looks lame to herðŸ˜)
Don't know what area you are in OP. If you are in the East Devon area then I can recommend a McTimoney practitioner who I use for both myself AND the horses (essential to do both IMO), she is based at Musbury nr Axminster.