Michigander - the Pro Elite uses the same e-clip as the TX200 as far as I can tell. It has the same part number, and the Airgun Spares site lists the TX200 part to also fit the Pro Elite. I ordered the last one they had in stock a couple of days ago.
My Pro Elite is apart right now so it's easy for me to measure the groove in which the clip fits. I get 4.06mm (measured) for the groove diameter, and 0.75mm for the groove width. The cocking link pin itself is 0.196" outside diameter (4.98mm) measured, which is likely a 5mm nominal diameter like yours.
From the PDF chart that you linked to, I'd look for a clip for a 4mm groove diameter and choose part DE-040 instead of the DE-032 clip.
I checked Mcmaster's metric e-clip offerings, and their part number 98543A112 is a little thicker and a bit larger O.D. than the Pro Elite/TX200 clip that I measured. The original Pro Elite e-clip that I have measures 7.19mm OD, 0.56mm thick, and of course fits my 4mm diameter groove.
I am going to place an order for supplies from McMaster in the near future, and I thought that I'd try their clips anyway. The measurements indicate a fit, and the extra OD of their clips will still fit in the flat on the breech. The best part is that 100 of them cost only $3.45 (plus shipping), so I thought that it would be a good experiment.