82 Z1000J The fun begins

Hi all,
As some of you guys already know I was lucky enough to recently get my hands on a Z1000J that was sitting in a shed for a number of years untouched.
I got a couple of hours over the weekend to play with the new toy and breath a bit of life into the old beast.
After draining the carb bowls, fresh juice into the tank, a new set of plugs and a fully charged battery it fired into life but only runs on 2 cylinders, #3 & #4, a little investigation and I can see I have a good strong spark on cylinders #1 & #2 which points me towards a fueling issue.
Checked the fuel flow to the carbs and all is good there so now I'm thinking pilot jets clogged up, because believe it or not I found a bundle of paper in the tank when I was draining it!!!!
So it's carbs off time to have a look and see what I can see. After getting them off the bike I can see that some muppet was at them at some stage already and has the tops of all the butterfly adjustment screws damaged, but the thing that bugged me is that they have broken the bottom of the butterfly adjustment housing on carb #1 (see the pic). It looks like it can be replaced but it's the hassle of trying to find that piece.
Would anybody happen to have a one sitting in a box on an doner carb that is looking for a new home?
The number I can find on the carb looks to read 1357 and they are mikuni carbs.
Any info on where to get one or these would be welcome before I start the search.
Thanks in advance for any help.