The Treasure Island SID you have is I think the C64 version.
What is available of the Xe03 homepage are the only known Plus/4 SID`s to me. Luca has a SID card for his Plus/4 and composed his work on his Plus4 making these very rare....
The tunes your after from C16/Plus4 games have never been made into any format for any PC/Amiga music player to use. They would need to emulate TED just like the replay of SID which is the emulation of C64.
The next best thing is to record the tunes from your real Plus/4 into MP3.
If your after some C16/Plus4 MP3`s, Amity added 4 back in Feb of this year: http://www.amity.amiga.tm/