Ok here is what I have found with stretched sprue: Firstly its very available, any piece of surplus plastic tree from a kit will do. Grab an old plastic tree, black is a good colour, silver is good as it is the right rigging wire colour really. Find a length of straight sprue in the tree, and cut it out. Must be long enough to be held with finger tips. Avoid sprue with a hollow centre. You will find some plastics better than others.
Heat source, a candle works great. Hold the sprue above the candle, turning it to evenly heat the sprue section.
Here is the art to it, the softer it is, and the faster you pull it apart, the thinner it will be. You need to play around with this, it is quite good fun. You need to make lengths, of the same thickness, may take a few attempts. But you can vary the thickness, as was the case on real aircraft, a thicker piece will represent a double rigging wire, quite nicely/acceptably, on a 1/72 kit.
For rigging to look good, it needs to cool dead straight. Nothing looks worse on a kit than sagging rigging wires!
It cools fast. Immediately after stretching it out, release one end and let it hang vertically for a short period, holding the one end vertically. It cools so fast you only need to hold it for a short period. This should allow for a dead straight piece of sprue. If you keep tension on it or take slight tension off it immediately, you will have a bowed length of sprue, useless to man or beast! I find the best way to get it to cool straight, is to let it hang under it's own weight, infact the piece of unheated sprue, acts as a slight plumb weight, keeping it nice and straight, as it cools. Lay it out straight on a flat surface. Lay it out straight, as this will also avoid it bowing. Choose the correct thickness on your stretched piece as it will vary, cut it from the rest of it, and you should have a length of usable dead straight sprue, ready to be cut to required lengths. Another reason to lay it out on a flat surface, is so you can cut it easily to do the rigging.
Measure the distance carefully between the struts of your model using a pair of old classroom deviders, allowing for a little overlap measure it out on your length of sprue and cut. Here is the tricky part, you need to gently hold the sprue with tweezers (grip too hard and you will kink the sprue), dip each end in white wood glue and position in place on the model. white glue is great, as it dries clear and shrinks slightly, putting a slight tautness on the rigging. It dries slowly, so you can move the piece of sprue about, to get it perfectly positioned.
You will find it quite good fun and you can do complex rigging jobs on 1/72 kits. On larger kits, it is tricky as if the piece is long, it can sag due to the white glue slow drying. Here is where super glue works. Glue one end to the strut, let it dry, hold the other end on the other strut, keeping the tension on, then glue it, gently holding the tension till the super glue sets. Trickier/fiddlier,
but does work.