You can always try cutting parts out of the numbers to make new ones.. but its not the most accurate of ways to do it.
you're best best is literally searchin google for nascar style numbers and fonts, there's bound to be a free one somewhere... or just start by checking deviantart.com dafont.com 1001fonts.com and go from there really
otherwise enjoy cutting sections via photoshop... e.g. for the top arch of a number 2 you could use the bottom of the number six for a rough guide....
hope that helps