Selling CITES I goods is under high rules within Germany, and the rules are much higher in terms of import/export (even for private persons). You need permission by federal states own ministries of environment or in some circumstances at least by the federal ministry of environment.
Just to add: this is not a special case in Germany, I have dealt with the same rules and documentary (which btw has been ratified by the EU in accordance to CITES which a lot of countries in the world comply to) so far with goods imported/exported from these countries:
China
Switzerland
Czech Republic
Poland
Slovakia
Checking for the UK, you need the exact paperwork, as in Germany or any other EU country and most countries which are complying to CITES listings:
Check if your import, export or re-export needs a permit or certificate under the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES).
www.gov.uk
That doesn't mean that some countries may have a tighter monitoring than others. But basically, selling, importing or exporting CITES I listed goods without paperwork is basically not legal in most countries and for good reason in my opinion. Owning the piece is not illegal.
I can fully understand that this is quite frustrating for the OP. From my experience with the local environmental department, they were very willing to help in any way. They even offered one time to accept a testimony from a witness to verify the legality of purchase of Brazilian Rosewood and prepared all needed paperwork for commercial use.
Therefore, I would just contact the responsible department of the country, where the goods are exported to and see, if they may have a solution or had similar cases before and know what to do.
I do not believe they would register your name on a blacklist and immediately seize you at the airport when you enter the country and check you for guitars
I would also contact the US Wildlife department and see, what their experience is. I mean, musicians are still using instruments with CITES I listed materials on a professional bassis for touring around the world (although most of them were made before the CITES I listing came into effect) so they must have experience with such cases.
Besides, at least in Germany we have officially approved experts who offer the service of examination of such pieces and are able to provide the needed documents after they have given their approval. This is common for vintage guitars, maybe such services are offered in the US as well?
