We have four foreign establishments registered with the USFDA and the one that is registered as the Foreign Exporter is also a Specification Developer and Manufacturer (from my memory as I'm not responsible for this anymore in detail) so it is difficult for me to demarcate the lines between the establishment types insofar as the QMS is concerned because they are seamless in practice.
So while the short answer is, yes, yYou have to comply as any Foreign Establishment would have to comply, which means you need to register your establishment, pay the fees, and identify the devices you are importing. , the longer answer is what that would actually involve if you are merely a Foreign Exporter. You may not even take actual physical possession of the medical devices and it seems like you don't reprocess or repackage or relabel. I'd work with your manufacturers and initial importers to do a thought experiment as to how they would Include you as part of their QMS and develop your own based upon that. You should probably get some consulting advice there as I'm just thinking aloud but your QMS should be simpler than most. But, as identified by Al Rosen, you seem to fall outside of the scope of 21 CFR 820.
You also might want to see if you qualify as an SME to save some registration fees. Unfortunately for us, while just our medical devices business could have qualified they took all our group activities into account so we pay the full fees.
Where I think you'll really run into problems, especially if your manufacturer(s) are OEM or private label is getting flagged in PREDICT for not keeping your FURLS database registrations maintained (edit: and shipping documentation in synchronized order). Also your customers' customers will probably want you to be a C-TPAT participant if you do any sort of volume into the US. Which will take work if you're not there already.
Hope this is somewhat helpful although my situation is different.
Edit: participate to participant
Edit2: added shipping document reference
Edit3: position reversal - agree with Al Rosen that the activities of OP fall outside the scope of 21 CFR 820