I think the reason that there's no commercially available PA28 calibrated dipstick is that it's hard to make an accurate measurement of fuel quantity in these tanks by the dipping method, due to the shape etc of the tank and the wide variation you get with the oleos/slope of the ground. I think that's why Piper put in the tabs, as being a reasonably accurate way of filling to part-tank, to allow a greater cabin/baggage payload. You can be down to over an hour's flying in a tank and not be able to see the fuel hardly at all. High-wing Cessna tanks seem better in this regard, though you get the dreaded fuel flow from one tank to the other with some models.
In my view, the proper way to operate fuel quantity with this sort of a/c is to work out the fuel consumption over a period of time, say, 50 - 100 hours, then use this figure to work out from full tanks (or from the tabs) how much fuel you've consumed. The fuel gauges' prime usefulness seem to be to fill in the holes in the panel.
In other words, your best fuel gauge/ dip stick is your watch.
Cheers,
TOO