ORA.ATO.150 from COMMISSION REGULATION (EU) No 290/2012 allows EASA IR training to be conducted outside EASA member states (i.e the USA)
When the ATO is approved to provide training for the instrument rating (IR) in third countries:
(a) the training programme shall include acclimatisation flying in one of the Member States before the IR skill test is taken; and
(b) the IR skill test shall be taken in one of the Member States.
There is only one school
European Flight Training which currently hold approval for this.