Welcome aboard Barnello.
You may be able to use the MTR Speed conversion decals for making the Gold Leaf 72C Lotus, but not sure they are still available:
http://www.macsmodeling.com/1-12%20STORE.htm
Or, try to buy new decals from Japan (Hobby Link Japan or Rainbow 10 Models may help). Tamiya have not re-run this kit for years so they may not have them though!
If you want to make you own decals you'll need a good quality correctly sized scan from the original decals. You'll need vectorised drawing software (like Adobe Illustrator) to re-draw them with separate layers for each colour, but it will be a hard job if you've not used it before as you need to have an understanding of print preparation.
You will also need to print onto decal paper, preferably using an expensive Alps printer as their inks are waterproof. If you are stuck with an inkjet printer you can buy clear and white inkjet decal sheets which come with a spray sealing varnish to stop the ink running when the decals wet. However, you won't be able to print the lettering in gold unless you use an Alps printer as they can print gold and silver foils.
None of the answers are easy I'm afraid!