As far as not giving him insulin for the week until you get some correct syringes…..I would try and source them earlier if you can. It is not a good idea to let a diabetic cat go without insulin, there is always the risk of ketones developing.
So what I would do is try and get the correct syringes …the U100 3/10 30 or 31 gauge 6 or 8 mm 1/2 unit syringes if you can asap.
In the meantime I would go out and buy a bottle of Ketostix or Dia-ketostix from a pharmacy that sells diabetic supplies and test Merlin’s urine for ketones daily…….this is an insurance against the ketones forming. Also make sure he eats well and if he goes off his food, or gets lethargic, that can be a sign of ketones.
If you can’t buy the syringes In Ireland…and I’m sure should be able to…..I will post a link to a place in the England that will post them to you
This is the link and these are the syringes you need
https://hyperdrug.co.uk/bd-microfine-insulin-syringes-0-3ml-pack-of-100/