A few things:
-First of all, which generation is this for, 3rd or 4th?
-This belongs in either the R/S/E/FR/LG or DP forum depending on the answer to the above. (A mod will take care of moving it)
-When adding something onto your original question when no-one has responded yet, you should edit your first post instead of making a separate post.
-And of course, welcome to TPM
OK, I can answer the shiny question. The only way for Sceptile is to keep trying. Each time you pick up or hatch your Treecko, there's a 1/8192 chance of it being shiny. There's really no special technique for getting a shiny, unless the pokemon is available in the grass in DP (then you can use the pokeradar trick). Of course, Treecko can't be caught that way, so luck is your only hope for getting a shiny one.