I haven't seen too many Herschel Walker cards come up for sale, that I don't already have, or that aren't next to impossible to get, because of low print runs, etc, but I was able to nab this 2019 multi player, jersey memorabilia card of a Walker jersey swatch, along with other Cowboy greats, Emmitt Smith, Troy Aikman, Bob Lilly, Michael Irvin and Bob Hayes.
This card is from the 2019 Leaf In the Game Used Franchise Favorites set. It is serial numbered, 23 of 35. The serial number can be seen on the card front, right in the middle in blue writing. There are several other variations of this card, with the same players, but in lesser print runs.