Your pto will have either 10 or 18 splines depending on the market that it was originally designed to be sold into. I have seen adapter shafts that slip over top of the existing 10 or 18 spline shafts that convert to the 540 rpm standard 1 3/8" 6 spline shaft on ebay occasionally. In case you didn't know, the B6000 pto rotates ccw which makes it tough to find attachments that will work correctly without modifications since 99% of all pto's rotate cw.
There is a company called Hub City that use to make a reverser assy for the B6000's but they are tough to find.
luckily the b6000 i just bought came with a bushhog so i ve got a drive shaft that i can use for other uses. when i figure out what those uses are. ive had luck finding weldable yolks ,shafts and such at parts houses in farming towns. just starting to have fun with mine though. later