Agree TOTALLY with using ash. A joy to work with (you need sharp blades) and really stable.

Have you tried REX Lumber in Acton? https://www.rexlumber.com/lumber/product/white-ash/

Even though they call themselves a wholesaler they are not likely to turn down a $400+ order. I was able to buy from them in the past but that was many years ago. Put your entire order together, generously allowing for waste, and include extra because you will fall in love with using ash and want lots of leftovers. Give them a call and make sure you use the correct lingo like 4/4, 6/4, 8/4, S1S, S2S, skip planed, rough sawn, etc. I wouldn't pretend you are anything but what you are. You're just hoping they could include your order on one of their trucks headed your way. You have nothing to lose.

Also if you are in NE Mass, you could try Highland Hardwoods- https://www.highlandhardwoods.com/lumber/retail/
They are east of Concord NH. I made the trip up there (I'm in SE Mass) years ago to buy all the Cherry for our kitchen when they had a sale.