I have an older alum tank (not sure of the size, about the size of a basket
ball) just for my BBQ. Paid $80 for it used but soon heard of the mandatory
OPD valve requirement. Checked a dozen or so refill/tank service stations
and none had the replacement valve for my size tank. Claimed they couldn't
find a stocking supplier..

I went on line and found my valve with a single Google and ordered it for
about $7. Took it to the refill/service station and they not only changed
the valve, but inspected and recertified my tank. Only cost was the price of
the refill..

BTW. To change the valve yourself is not something to attempt yourself since
you will have to hold the tank somehow while you remove the valve. This is
complicated by the valve guard. Once changed the tank should be inspected
and recertified. (If I were the operater of a refill facility, I wouldn't
want to risk filling DIY tank/valves.) These tanks require periodic
recertification anyway and most gas suppliers will do it for free or a small
fee.

My opinion and experience, FWIW.

Steve
s/v Good Intentions