Col - Welcome! First of all, for Wild Bunch (WB) the 45 ACP ammunition has to be lead bullets.
Looking around the Internet for you, here's the best price I could find for you at Buffalo Arms, which is in stock ... http://www.buffaloarms.com/45_ACP_Ammunition%20_it-1080901.aspx?CAT=4439
Only a couple of other vendors with 45 ACP with lead noses - but double the price
You might want to also read the Wild Bunch Rules Handbook ...
http://www.sassnet.com/Downloads/RO/Wild%20Bunch%20Handbook%20v7_1.pdf
If you are planning to reload:
* Buy once fired 45 ACP brass
* 1000 bullets - 200gr
* Large pistol primers
* Unique or Red Dot powder (if you can find either now)
* Dies and a press - your in business at less than 1/2 the cost of store bought