I suggest you buy some recorder music. Obviously if you want to play in a group you'll need to transpose (all recorder music is in C), but as a solo instrument it fits the sax well. Soprano/tenor recorder music has a range from C0 to C2 and alto/bass music has a range from F0 to F2. So look for recorder music books from the time period you are interested in. And you can go to IMSLP.org and look around there for free downloads of early music.
The other thing is that there was not a lot of specifically wind instrumental music written out before 1600. That is why the van Eyck collection mentioned above is so unique as it is specifically written for recorder. Groups like Piffaro and the Baltimore Consort will give you other ideas of what to play. This also means you don't have to worry too much about the authenticity of playing early music on sax: back then the instrumentation was not fixed too often.
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