The numbers go up to over a thousand in most sections.
The only way to find it is basically to walk up and down each row and see if you can find a number on any of the stones - the number (if there is one) is usually on the base somewhere.
It'll just be a case that when you find some numbered stones, you'll have to try and figure out how the rows run.
Alternatively, if you visit during 'office hours', try the wee office which is at the next entrance up next to the Crematorium in the Western Necropolis. If all else fails, and you can find/see any maintenance men, they are very helpful, unless of course they are attending at a funeral.
Anne