Sometimes, when I am looking for rare sheets, I will see if any recordings have been made. If so, I then write to the publishers and ask where they obtained the scores.
Thankfully, some of Albero's sonatas have been recorded and you will find this doing a simple google search.
It is also worth posting a request on a site such as Gamingforce, as you will be amazed what some people have.
Another tack would be to write to the Portuguese National Library, or a Portuguese Music Publisher like Musicoteca.
If all else fails and you have a credit card with a 6 million dollar credit limit, you could order the sheets from the British Library who do hold these sonatas.
Happy hunting.
Thal
PS, if you do find them, can i have a copy for my collection
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PPS, it is on sale here and therefore probably others.
https://www.musicroom.com/search.aspx?searchtext=albero&searchtype=all
Topic: Sheet request