I had a customer asking about things like that recently, and was doing some research into the subject. Getting accurate reference material for the earlier dates is remarkably tricky, it must be said. Some of the examples are very curved, some are much closer to being straight, however.
Also such a tool would only have been used in conjunction with a bone saw, as depicted in this slightly later (16th C) woodcut:
I also would note that Will.S' suggestion for making one rather lacks a number of very significant essential elements - namely:
first, getting the right sort of steel and thickness (3-4mm carbon steel plate - sheet will not do, and the sort of mild steel you can buy from ebay or most stockholders will not do the job, as its is soft and does not have any spring properties - meaning it will not hold an edge, and if bent it will stay bent. Such steels cant be used as they cannot be heat-treated, you need something like 1070/CS70 spec steels which would do the job, and come in suitable plate for stock removal. O1 or EN42 would do it better, and could be forgeworked to shape.
Second, the actual shaping work would need to get a consistent bevel on the shape, (for which a file on a concave edge is going to be an absolute nightmare without a lot of experience) so its going to need to be linished and cleaned up.
Third, and the most important stage would be the heat-treatment of the steel to harden the blade by heating past its austentic point, (ie, glowing orange-yellow hot) and quenching ( most likely into oil for most of those carbon steels, a water quench would be likely to crack the steel.) and then tempering to make it less brittle. And of course, after which all the finishing work to polish it and surface the steel would need to be done to clean up and turn it from some ugly "muddyevil" bit of blackened metal into a nicely finished blade that looks accurate. Edit: if you are DIY-ing it, and the idea of delving into the black art of metallurgical heat-treatment and forges leaves you rather daunted, you can get pre-hardened CS80carbon steel plate in 3mm or 4mm thicknesses from Steve Sawford at BSS Steelstrip for about £70 for a sheet 90cm x 30cm in size. That's easily enough for 2-3 such knives with plenty left over for smaller tools. But be warned, file-working that sort of metal in its hardened state is likely to be an absolute nightmare. I would struggle with doing that, and I have a £1000+ industrial linisher that's built for making steel blades. With just a file, it would likely prove impossible - the file will mostly skitter off that and not bite. you would need power tools like a grinder, dremels, and the likes to shape it.
Lastly, there is the fact that for any knives between 1000 and 1375-1400, it would certainly not be made with two pieces of wood on either side of the tang, (a scale tang construction), but would in fact be a whittle tang construction, of one single piece with a slot into which the tang of the blade was attached. No examples of scale grips exist prior to about 1375.
If you'll excuse a website of my work, these knives should give an example of what handles would've looked like: http://elmslie.co.uk/projects/Eating_knives_nov_13_01.jpg
the top two knives in that pic, with wooden scales are distinctive of the 15th century - cherry and holly scales pinned in place using brass/latten or bronze pins respectively, and with small bolster plates soldered onto the blade that the plates line up with. The bottom two knives are earlier, 13th and 14th century fashion, and consist of boxwood (which is what most scale grips would've been made from too - particular in England.) and from horn and holly on the bottom one. As you can see, unlike the top two knives, the tang of the handle isnt exposed, but has material all around it, and it is driven into the handle (which is pre-drilled and then shaped to fit) and secured with cutler's resin.
Hopefully that'll give you some pointers in what is needed for making such equipment. If you'd like more advice, or if you'd like to talk about such an item being made properly, I'd be happy to chat about it.