Does anyone have suggestions for places to purchase pre made butter cream large  Amount. I have used the Wilton tub but it's not my favorite kind of hard to work with I just need more than actually want to make lol

Do you have a Sam's Club near you?  I'm pretty sure they sell large quantities.  If there is one near you, you could always give them a call.  Of course you will need to be a member to purchase from them but it might be worth it if you need a lot of buttercream/baking ingredients on a consistent basis.

It’s soooo easy to make Why are you buying ready made?   Try the recipe “2 of everything “ in the recipe section of this site    

Another option is to add lots of extra vanilla  — about 2Tablespoons to 4 cups)  & instead of the liquid you are using add UNflavored (plain) yogurt to the icing & mix (not beat) well

Thanks. I will check out these options

Kakeladi - what does the yogurt do? Is it just to cut the sweetness? Would it affect shelf stability? 

Yes, it helps cut the sweetness and thins it some.  No it does not affect shelf life at all.  Usually you are only using a couple tablespoons or up to 1/4 cup compared to4 #s of sugar.