AFAIK you do not need a Mainland Resident Taiwan Travel Permit if you hold a permanent visa from a third country. If you're still unsure, I suggest that you contact the Border Security people from the port where you will exit China. They should be able to set you straight.
OK I was wrong. The only situation where you can fly direct to Taiwan without a permit is if you have an onward ticket to your country of residence. If you're transiting from Taiwan to a third country or if you're returning to China from Taiwan then you must have a Mainland Resident Taiwan Travel Permit, which as you said cannot be obtained in your case.
The only alternative for visiting Taiwan from China is to travel via a third country, and most people would choose Hong Kong when starting from China.
Last edited by tauphi; Feb 19, 2019 at 8:41 pm