Here's what I have learned, it may be different from CRH'er to CRH'er...
Unless you have a REALLY deep relationship with one bank, it will be hard to dump mass quantities of halves. Fact is, there is no profit in this for the banks, just the cost of labor/bags/machine maintenance. And as a general rule, tellers hate to deal with dump coins, change bags, go to the vault, blah blah blah...
Here are my tips on how to get through some serious volume each week...
1 - open up several savings accounts with multiple mid-to-large size banks that have multiple branches in your area. I have four accounts and access to about 10 different branches.
2 - have each branch order you $1k in halves each week.
3 - limit your pick ups and dumps to only $1k per bank, per week
4 - bring the tellers a little treat every month - fun size chocolates have produced MANY one-off silver dimes/quarters/halves for me
5 - when they ask, be honest with them and tell them you collect and are trying to fill up the folders and also looking for any type of older ones.
6 - get to know a few tellers at each location, the more they talk about themselves, the less they ask about you :-)
Spread out the work, be a decent human being, and stay engaged with the people who help you at the banks. This way, when you bring an extra bag to dump that you picked up in TinyTown, USA, they will gladly accommodate your request...