Unfortunately, I do not know of one. However, I would really like to see a site provide old Taiwanese songs such as U Hiao Hue (Rainy Night Flower), Pang Chhun Hong (Waiting for the Spring Wind), Kio Tio Gua (Calling Me Home), and Mama Chh*ia Li (Mama, Please Take Care).
I don’t think copyright will be an issue, as many of the studios and companies that produced these songs have long since closed, and given Taiwan’s deficient intellectual property laws, the copyrights will have lapsed into public domain. Ie, these songs were produced during the Japanese Era, when ROC laws did not even apply to Taiwan.
Whether the copyright can be passed on to any surviving heirs, after the original entity has closed and after the issuing government has relinquished sovereignty is a highly theoretical question that Taiwanese courts will not be enthusiastic addressing.
If someone is willling to host such a site, I can send my MP3 collection of these songs (for fair use and educational purposes).