Okay, so what's the deal? Are both of these correct :
Chan eil mi ag iarraidh dà mhuc.
Chan eil mi ag iarraidh dà mucan
As far as I know, you don't use the plural form after "da".
Correct, this point is made in the Tips - singular form after aon and dà, as well as cia/cò mheud?
And, separately from that but just as important, dà, like aon causes lenition, hence the mh.