I cannot find anywhere bow saw frame for 42 inch blade. Could you advise? Many thanks, Martin
These days I think most bow-saw frames are made by the woodworker and not bought, although that may be just what is common in Western Europe and North America.
If making your own sounds like a project you'd be interested in here is a plan you can use as a starting point, scaling up as needed for the length of your saw blade:
For greater details of a different frame style look at this article on Popular Woodworking, Make a Shapely Bowsaw.
Another option to consider which vastly simplifies the making of one is simply by fitting the blade to two ends of a bent branch: