Hi Minh. You can make rings on your homemade lathe, they're not difficult to make really. There are many methods described online, from very simple to very involved, I tend to make mine very simply. They don't seal perfectly at first, but good enough to get the engine started. Then over the first 10 minutes or so of running they wear in (or 'bed in' if you prefer) and compression is very good.
The method I use, just for your reference: Turn the OD of the ring blank to the exact bore size, then bore the inside of the blank to what ever size you've worked out for required ring thickness. Then part off slightly wider (maybe 0.001" or so) - when I part them I have a rod in the tailstock into the bore to catch them as they drop. Rub each side in a figure 8 pattern on some fine sand paper on a flat surface to get to the required width. To snap the ring you can use your finger (but you might break a few until you work it out) or cut through with a saw. Then you need to place a 'wedge' or spacer in the split to spread the ring a little (the width depends on the size) and place the rings on a large washer or something like that - I use a car body washer held horizontally in my vice. Heat the ring with a propane torch evenly to bright red and keep it there for a minute or so, then let it cool naturally. When the spacer is removed the gap should stay the same and the ring now has tension. File down the ends to achieve the required ring gap when it's installed and it's ready to go. I normally make at least twice as many ring blanks as I need and just split and heat treat the ones I need, keeping the others as spares.
For the fuel, I forgot to mention a lot of people use something called Coleman fuel which I'm told burns cleaner and smells nicer than normal petrol. I don't bother as it's hard to get here and I only run my engines outside once they're finished.
Good luck with your build. I'm hoping you'll post a build thread with construction photos as you build it.
