The simplest way is to pull out a current brake pad and read the model number listed below the name.
The current Vado SL 5.0 specs list Tektro HD-R510 brakes
The current Vado Sl 4.0 specs list Tektro HD-R290 brakes.
Go to the brake pad finder on the Tektro site and look for your brake model.
https://tektro-usa.com/brake-pads-finder/
The pad finder gives you the pad numbers. For example, for HD-R290 brakes, compatible pads are: E10.11 A10.11 A10YS P20.11 A11TS
You can now go to ebay, amazon, etc and do a search for Tektro and (pad number)
On the Tektro website (products - disc pads) you can get a brief description of each pad
I see that the E10.11 pad description states it fits all the brakes listed below. Therefore the HD-R290 brakes can use the same pads as many of the other brakes sold by Tektro.
HD-M740 / M730 / M520 / M521 / M510 / M500 / M501
HD-M290 / M291 / M285 / M286
HD-T710 / T520 / T530 / T290 / T285 / T525
MD-M500 / M300 / M280
MD-C510 / C400