Ebay is a fantastic source of everything. I got mine about two years ago, from some pub somewhere or something. I don't know. About £40 delivered, anyway. It worked fine for a year (that's about 3 brews), before it started pumping more beer out from the piston seal than it did from the spout. I finally ordered a new seal set for it last week.
Seal kits are a little expensive. I'd say about the same as their weight in gold. Crap for a few bits of rubber. But they are very unique bits of rubber, and at £28 delivered, you'll soon realise you'll make the money back in sheer joy at not having to wipe the carpet after every pour.
I'm not going to go mad on the detail here, but hopefully the following pictures will help you see what's inside of a Higene beer engine.
The key is to put it back together EXACTLY as you took it apart. Take photos or draw or arrange neatly on a table. Mostly it's fairly simple, but the cylinder needs some care.
If you buy one new and it's not working great, then force some water into it (with a hosepipe is best), and let that sit for a while to loosen up the rubber seals a little. You might find it works fine. You'll still want it taken apart and cleaned. You'll see why when you do it.
I've replaced the pipe from the top of the cylinder with a 3/8" JG to 3/8" stem (elbow) and a shorter piece of braided hose. It works much better than the bit of kinked hose, and the original hose was black with age.
These pictures really aren't in any order.
The key is to swear a lot when putting it back together.
When fixing it to your bar (what do you mean you don't have a bar?) it will be quite rough on whatever the bar top is made of. Not in a scratchy way, but in a "if your bar top is not nailed down properly it's coming off" kind of way. Also, it only goes half -way on, so cutting a slot out of your bar top will support it better, but it's not strictly necessary. I'll post some pictures of my bar towards the end of summer.