Uncle Jaque,

Be very cautious about old German instruments - they were made for a very cheap end of the market (except for the bandoneons - the multi-multi buttoned square monsters beloved of Argentine tangoists- who call them concertinas - and mid-westerm Polish polka players). The top quality is found in English-made instruments but at a vastly greater price. Old ones that have survived from the 19th century are going to stay around for a lot longer. The Italian factory instruments of today are not too bad but a lot less lasting, with bellows that won't last as long and some dubious key actions (some importers do some degree of rework on 'special' models).

If you want an anglo based around a D/G structure you are only going to find that in a new and very expensive English-made 30+ key model (Thousands of dollars!) unless you have the skills (or helpful friends) to rebuild a 20-key G/C to a D/G as I have done.

BTW: Never patch bellows with tape - when it does finally fail ... with mastic destroying all the previously redeemable fabric ... your concertina repairer will beat you to death! A bellows infected with tape can never be redeemed.