Every now and then, I have seen them pop up in ebay.
Just search them as "150 pin card edge connector"
Just be carefull to select the one that has proper pitch (separation between pins), and correct layout.
In the past I have seen some at about $15 each.
Another solution is to contact Jens Schoenfeld at Individual Computers, and ask him if he could sell you some of his stock.
Good luck