Andrew.
I have a copy of "Popular Woodworking Finishing & Refinishing". There is an article on wipe-on finishing. In the article there is a piece on Making your own.
You can easily make your own wiping varnish or oil/varnish blend. To make a wiping varnish, thin any oil-based varnish or polyurethane with mineral spirits (paint thinner)until you reach a thinness that's easy to wipe on. The higher the ratio of finish the faster it will build, so begin with as little as 25 percent mineral spirits and increase the amount if this doesn't give you enough working time.
To make an oil/varnish blend, mix any brand of oil-based varnish or polyurethane varnish in any proportion with linseed oil or tung oil. The higher the ratio of varnish you use, the glossier, more protective and durable the finish. The higher the ratio of oil you use, the longer the working time.
If the mixture is to thick for your tastes, thin it with mineral spirits. As with wiping varnish, it doesn't take much thinner to make a big difference in the viscosity of the finish. Commercial brands of wiping varnish and oil/varnish blend are thinned far more than they need to be.
I hope this is of some help to someone.
Good luck.
ATB Gary.