Whilst you don't make it clear, your mention of the Bristow Academy suggests that you are looking for the JAA IR(H), in which case there are no training providers in the US that hold such approval. If, on the other hand, you really meant the IR(A), a cursory check of Standards Document 31 quickly reveals that there is only one training provider in the US approved by the UK to conduct such training - European Flight Training in Fort Pierce, FL.
AFAIK, all other JAA states comply with Appendix 1b to JAR-FCL 1.055 and approve only integrated training to take place in non-JAA states, although this could have changed recently and you would have to check with the JAA or individual NAAs to be sure.
Contacttower is incorrect in his ill-informed assertion that IR training cannot take place outside the JAA. It is only the IR Skill Test and, common sense dictates, some acclimatisation flying that must be completed in a JAA member state.