It's really not that hard to calculate yourself.
The quick and short answer is 224 HP EVs to get 336 HP.
How you can calculate yourself is as follows:
1. Put your Scizor's IVs into Smogon's Damage/IV Calculator (basically the only one that matters is HP for you, so just change the default 31 HP IV to 30).
2. Put 252 HP EVs and see what stat you get for Scizor's HP (343 in this case).
3. Punch that HP number (343) in your calculator and divide it by 16, and then round down to the nearest whole number (21).
4. Multiply by 16, you get 336.
5. Put 336 in the HP Stat for Scizor, and Smogon's Calculator will tell you that you need 224 HP EVs.
Hope that helps.