There's a musical instrument shop in Rua do Brasil(town end) in Coimbra a few doors down from the Colégio do São Teotonio.(The long road that runs by the Dolce Vita Centre and Académica Stadium) I visited it when I was involved in organising Dance Coimbra 2012 last year.
Rua do Brasil, nº71/73,
tlf. 239 798 420
fax. 239 798 429
Online Accordeon Dogalogue(not fond of cats and trying to avoid be speciesist! ) here:
http://www.lojamusica.com/produtos/cate ... rdeao-363/
In Porto, there is are several. There is what appears to be a good one close by where we often stay when in Porto. (closest metro station: Metro Carolina Michaelis)
Avenida da Boavista , 25 - Boavista
22 600 7830
Online Accordeon Dogalogue here:
http://www.ludimusic.com//produtos1.asp ... i=EUR&p=PT
Most towns of any size in Portugal will have a music shop and if they don't have what you want they can probably get it for you.
P.S. Just found one in Lousã:
Praça Francisco Sá Carneiro 39 3200
239 992 739