Does anyone know the sizes for NightForce SHV 3-10x42 ???

If you print page 3 of this guide it shows a way to measure them.

Otherwise I looked at the chart towards the back half of that guide from Butler Creek.  According to NF your eye piece is 40mm and the objective is 50mm.

Looking at the same size objectives this is what I find:

40mm:
MultiFlex  -  #13/14
Flip-Up - #13
Blizzard - #4

50mm:
MultiFlex -   #30/31
Flip-Up -  #30
Blizzard - #8

Don't quote me on this, but I based those off of other scopes on the chart.  I hope this helps.

Take the scope into a store that has the Butler Creek covers. I've found the chart is often wrong, especially for the objective end.  Look up what appears to fit but go in and double check.

Believe me I know many times.

Thanks for the feedback gentlemen! I decided to not buy the SHV due to the fact that I had to dig and find out it is a made in Japan scope. Which is not awful news but for 888 dollars shipped I could get something from Leupold made in the USA with the same warranty. I'll just have to do some more saving and look into the nxs series.
But again I do appreciate your help.

No problem at all!  I highly recommend the NXS series if you can swing it.  I absolutely love my 2.5-10x44.  It was absolutely worth saving up for.