The only ones that come to mind are possibly; Hayle Bird Garden in Cornwall- they have a dozen Lears Macaws though split in to pairs in several aviaries. Plus the other macaws and cockatoos are in good number too though not in 'colonies' as such. Then there is that parrot rescue place in Lincolnshire- they have dozens(hundreds?) of ex-pet macaws and parrots, mainly Blue & Yellow, and Green-winged, African Grey etc I think. But most/many will be humanised ex- pets so perhaps desocialised with other parrots(?), in which case despite the numbers they wouldn't count as colonies either.