How do I invest in an index fund while resident in the Cayman Islands?

I am a Brit living in the Cayman Islands, how can I invest in an index fund (SPY, Vanguard, or Fidelity)?

I have an account set up with interactive brokers but it says I cannot buy fidelity (FXAIX) due to my residency.

Does anyone have any experience with this issue? Would really appreciate some help pointing me in the right direction. Thanks.