There is no current policy that I could find that mentions a $10K threshold. Could you provide a current policy that established the $10K MPT? Also, why would a $10K MPT be in place authorizing $25K from overseas vendors and only $10K from US based vendors?
It seems we get a lot of GPC questions here at AAP.
Your local contracting office policy is correct and compliant with the Federal Acquisition Regulation (FAR), Defense Federal Acquisition Regulation Supplement (DFARS), and the Department of Defense Government Charge Card Guidebook for Establishing and Managing Purchase, Travel, and Fuel Card Programs.
The DoD Guidebook [see paragraph A.1.2.1.b) on PDF page 32] explains the Simplified Acquisition Procedures outside the U.S. as does DFARS 213.301 and DFARS PGI 213.301. It limits GPC purchases to $25K if outside the United States and outside of U.S. Jurisdiction. Contractors located inside the U.S. are by default inside the U.S. and subject to U.S. jurisdiction.
The DoD Guidebook [see paragraph A.1.2.1.a) on PDF page 32] explains the GPC can be used for purchases up to the micro purchase threshold (MPT) as does FAR 13.301(c), and DFARS 213.270. (Note: I did not link FAR and DFARS references but you can find them easily enough using any internet search engine of your choice.)
The FAR and DFARS have not been updated to reflect the authorized MPT (but that is too long a story to discuss here); it is reflected in DoD Class Deviation 2018-O0018. Note there are 5 definitions of the MPT, but that is beyond the scope of this question.
As a reminder, you should also review the DoD Guidebook paragraph A.1.2.4 – Prohibited Purchases.