Martin
scrounge whatever hardware you can for assembly.? if you don't like this plan, there are several fine suppliers of cases aka enclosures available.?
if you have a 'surplus. electret based microphone - try it out.? I am using something once used with an HT I no longer have.? use a search engine here or on the web to see what others are using with the BITX.? Pacific Antenna in US has a microphone kit for these rigs - but its nothing you can't homebrew from the electret microphone furnished with the kit or available on ebay etc.?
do enjoy assembly of the fine rig.? the beauty is having it your own way as you assemble it, and a wealth of ideas from a world-wide community of builders.?
Curt