First of all certificate of non issuance is not the same as police clearance certificate. Also CIC or MPNP officials will not issue any letter in order to get a police clearance certificate. If you really need a certificate of non issuance letter from Detroit office, you have to show all your paper works from MPNP and CIC that you are planning to migrate to Manitoba and it is very necessary for you to get a certificate of non issuance letter.
2nd option, You can find the local police station in Iraq, your husband used to work that area. You can call them and get an instructions to obtain a police clearance certificate during that time 2002-2010. Also you need to explain to them about getting a police clearance certificate and you need to show all paper works that your husband used to work there. (e.g; payslips, bank statement, home address correspondence, bills etc.) Just bear in mind police clearnce certificate is not necessary to submit at CIC initial application stage, you may submit it later before getting your visa to Manitoba. So, you have some time to sort out this problem. Always, where there is a will, there is a way. Thank you.