If the military reserve exchange programme (https://mrep.mod.uk) survives contact with the pandemic, the recession and the integrated review, then there are opportunities to get embedded in US Guard and Reserve units for up to 4 weeks. But you have to be a full screw in order to meet the SQEP criteria of the H&S legislation.
Other than that, there is the routine OTX programme (assuming that doesn’t get bandied in the name of progress) that gets rotated around units. Destinations include Cyprus, Italy, France, Denmark, Australia, Spain and, err...can’t remember the others, but that are all ‘Star’ exercises (e.g. Iberian Star).