I understand that the owner of Na Ruixa is from Galicia, in the north of Spain, a place that is well known for its sea food and for its octopuss dishes.
Maybe he could be of help.
The main fish market in Palma sell live ones if you want to try yourself !
Would have to be El Posito for all types of Octopus and Squid, especially their Calamari, which is simply outstanding, certainly the best in The Port, (and there's not many establishments where I haven't sampled it).