We did that on an earlier m/home, if you have the origionals (never mind the condition) your local carpet company will be able to cut new carpet that you choose to pattern and either bind them in house or they will have an outworker who will do them.
If you do not have the origionalsjust buy some of the paper stuff that goes under the underlay and cut patterns from this. If you go and talk to a friendly carpet shop and choose your carpet first you may well find they will give you an offcut of the paper stuff for free, they did for me.
The binding is, relatively, expensive but you can understand when you see how time consuming it is to do.
One tip I would add (from bad choice and experience) is get good Hessian backed carpet, do not use any with foam back, you will find it quickly disintegrates and leaves powder all over the place, especially if you remove and roll it up regularly as we do!!