I have recently purchased a cyclocross frame to take front M15*100 and rear M12*142 thru axles. The frame has no thread in front fork and rear for the thru axles. What axles do I need to purchase and where are they obtainable?
This strongly suggests that the frame and fork have removable/replaceable threaded bits. There aren't really standards for these; they're more considered part of or specific to individual frames/bikes. It's the kind of thing you tend to have to get from a dealer for that brand or in some cases direct from the manufacturer. If this is the case, once you have them you would be able to measure the effective dropout thickness on each side and from there you'd be able to add those numbers to the spacing, and then you just buy a thru-axle that long with the right thread. Or you could just get them from whoever you get the frame fittings from.
There are some thru-axles that are unthreaded. Suntour Q-Loc is the main one running around currently that I've seen, but it's pretty common. However, it's only on suspension forks that I know of, and not on road/cx bikes at all, so I doubt it's what you have. But if the frame and fork feature a long, plain bore where something might fit through and don't look like they're missing anything, it's possible it's something like this that you need.