I need to replace one of my balls

I just picked up a vintage, wooden, Arriflex tripod and head. Great condition, only the ball on the end of one of the lockdown levers is missing. I found this one online for 75 cents. But shipping was over $11. (Also, it looks like it goes onto a 6mm bolt, and I think the levers have 5mm threads.)

Rather than pay a bunch for shipping, or go to every hardware store in town to see if they even carry such a thing, I thought I’d ask for leads here. Who might carry threaded metric knobs? Harbor Freight? Some other national chain?

Here’s 5 for $4.51 with 5mm female thread on eBay: http://www.ebay.com/itm/Equipment-Tool-5mm-Dia-Female-Thread-Hole-Black-Plastic-Ball-Knob-5pcs-/231120803353?_trksid=p2054897.l4275

Thanks! I’m ‘watching’ it until I can verify the thread size.

I just got back form the hardware store, confirming the M5 threads by screwing my knob (heh) onto their tester and a bolt. Turns out the knobs in the link are 25mm, but the same seller had a package of four 20mm ones with M5 threads. So whenever they get here from Hong Kong, my tripod will be complete! (It’s also missing the pan handle, but it will be here before the balls. Not Arri, but this is a tripod that is going to be used; not just something for the collection.)