All aircraft (AN) hardware should have "locking" features, such as self-locking nuts, safety rings, or safety wire. You can NOT tighten hardware enough to "secure" it on our gliders, in most cases; if you try to do that, you will just crush (oval-ize) the tubing, which makes the tubing weak. Use the correct hardware, with reliable locking features. Fair Warning: Not all HG manufacturers use bolts long enough to engage the locking features of AN locknuts.
Aircraft self-locking nuts come in two flavors. Nylocs (Nylon locking nuts) are good for one use only; once you remove it, then you should trash it, and use a new Nyloc to replace it. All-metal locking nuts are re-usable; they come in several varieties. Any AN-grade locking nut which does not have two or more bolt threads showing above the nut is NOT properly locked. That is because AN bolts are tapered, for the first few threads, and the nut needs to grip the bolt threads strongly, at their full diameter, and not weakly, at just the tapered threads.
Aircraft (AN-grade) bolts can be had with a hole through the head, and/or a hole through the threads, for safety-wire or a safety ring. Here is a down-loadable bolt sizing chart, in .PDF format:
Prefer safety rings over safety pins, because safety pins can spring open if bumped, or otherwise given the chance; safety rings will spring closed. This difference is very important. You can bend a short "entrance ramp" into the end of a safety ring, to make it easier to get started into a pin-hole. If you trace the path of the wire around the ring itself, the last millimeters of the wire should veer inward, forming the "entrance ramp." This trick makes safety rings fairly easy to deal with, without compromising their function.
Aircraft safety wire is typically 0.032 inch (~0,8mm) diameter, Ni-Chrome (Nickel-Chromium) Stainless Steel wire. It is very rust-resistant wire.
A good "nut-and-bolts" shop may be found in the phone book (anywho.com in the USA) under exactly that heading. A good search engine may do the job, as well. Local airports may sell AN hardware, or try the aircraft supply houses. Aircraft Spruce and Specialties, and Wicks, are dealers for AN-grade hardware. They can usually ship overseas.