Costco used to have boxes of syringes out in their display cases. They
were for diabetics and insulin but they would work for urine too. Haven't
seen them for a few years but I too wish to inject it and am going to ask at
Costco at the pharmacy counter. Think they pulled them from display to
keep the druggies from getting them. They should also be available at most
drug stores - and Amazon.com carries them too.
I've seen urine injection in a video. It shouldn't be difficult.
Just use fresh. Here's a little blurb that says "it's easy."