For the head you could use the DID Afghan figures or soldier story Iraq figures, or, seeing as there were members of iSIS of caucasian heritage, any sculpt. Clothes….again, either DID Afghan figure or any civvies i guess
It really depends on where they are and how far up the chain of command they are. If you do a search for "isis uniforms" you should get a decent variety of moderately standardized garb for various locations. Then once you have one picked out that really appeals to you, just search for the different articles of clothing, etc. and add 1/6 to the search criteria.
I used to have an ebay seller named Luis who was my go to guy for anything specific. Sadly he stopped selling, so I really don't have a recommended source for gear to give you.
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