Margaret, 'as many as Dan' refers to the people sending as many babbies to Her Majesty, produced in the traditional way, as Dan (Daniel O'Connell) can send, supposedly made by steam.

I've heard the line as We'll be able to send her a lot more than Dan.

(I've also never heard the phrase 'as many as damn', being used to mean broadly 'a helluva lot'.)

Great song!!