USPS Registered and Insured. Have a local FFL take it to the Post Office with you. Have him do the shipping and you reimburse him for the postage and his service.
Post your target price. And no, I do not have one to offer you.
Here was the last HK 93/33 conversion I saw on GB:
EXTREMELY RARE UNICORN HK FACTORY SEMI -AUTO HK93 .22 CONVERSION KIT! - Other Rifle Accessories & Parts at GunBroker.com : 975553662
Seller and buyer in different states: Seller Form-4 to SOT in buyer state. SOT in buyer state Form-4 to buyer.
Seller and buyer in same state: Seller Form-4 to buyer.