As we do not know exactly what you allergic to (you said coconut but it could be coconut milk, an additive in the milk or coconut in general), I will make some extra suggestions:
1) You might be able to try adding natural coconut flavouring to the already mentioned nut milks (cashew or almond). This might tip the scales in making an Indian style almond based curry taste like a Thai coconut milk based curry.
2) If you are allergic to everything coconut then you could try Imitation Coconut Extract which shouldn't contain any coconut. Again, this might tip the balance on the other nut-based milks.
3) You could try adding gorse flower extract. I have never tried it but I do know from roaming the coastlines and moorland of Devon, that gorse smells a lot like coconut. It is edible, is common year-round and according to eatweed.com, has a subtle coconutty taste. I see no reason this could not be added to a curry to infuse further coconut tones.
Finally, if you are allergic to all coconut, here is a quick and helpful guide to replacing all coconut ingredients.