As an Amazing Blondel appreciator (Fantasium Lindum is still my favourite LP of all time!) I do know that Yaddlethorpe does indeed exist, as do there many towns ending in 'thorpe but as to whether there was ever a seige I am not so sure. Busy Bee, please do tell me if you ever find out about this "seige".
Indeed, the final track on the album England entitled Lament to the Earl of Bottesford Beck also alludes to a real place; that of Bottesford and I am only assuming that there is a beck that runs through said village/town.
I have not seen the plastic crumhorns for some time but I can recommend Moeck, Eric Moulder (possibly a waiting list) and the Korber's the latter of which can only be found second hand and they do crop up from time to time (in the region of £250 or so for a soprano or alto). Get in touch with the Early Music Shop in Bradford for their newsletter to see if any are available.
Of course the range is more limited than a recorder as Wilfried says; it was intended as a consort instrument back in the rennaissance to be played as part of a soprano/alto/tenor/bass group.