When I'm mixing things together I use a 1ml syringe I bought from the pharmacy. It's the type that are commonly used by diabetics for injection of insulin so are readily available. It will quite likely be neccessary to explain or maybe even show the pharmacist what you need them for, They can be very cautious about selling syringes and needles to the general public.
In general I make up quite small amounts when I'm "playing" with flavour combinations. Typically that is 2-3ml only so I'm not wasting to much
juice on failures. The 1ml syringe makes it very easy to measure accurately the small amounts involved.
I have several syringes and am careful to keep them separate when mixing, 1 for each component. Cleaning is also a big part of it, I was them out using hot water and detergent and then a plain hot water rinse. Every so often I take them completely apart, barrel, plunger and needle and boil them in water for a few minutes to really get them clean and more or less sterile again. They do wear out after awhile and go back to the pharmacy as they have a sharps disposal service, and I get some more.
5ml syringes can be bought as medicine dispensors from most pharmacies, these don't have a needle though. That makes it a bit more difficult to use them, but they do still work ok.
I forgot to add. I make my mixes in some small glass pill bottles I also got from the pharmacy, they are probably 15ml in size, brown glass and work very well. The brown glass is important as nicotine is photosensitive and breaks down in sunlight. Opaque plastic would work too.
My mixing bottles have straight sides and a wide mouth, that makes it easy to get the syringe in them.
