I originally knew nothing of sketch cards and their existence prior to starting my first set which was a Walking Dead Evolution card set for Topps Cards and I didn't know that they inserted them into packs of regular trading cards as rare original sketch card items.
So above is one of the main ways to get into actual companies and do freelance sketch work for them and it's easier than you think. All you do is contact these companies through their social media pages or if you know other Artists that are doing cards, aks them to see if they'll give you the contact details.
I was lucky, another Artist referred me to Topps and then I found other work later on through other places that I networked with through Facebook groups mainly.
Here are just some examples of the cards I have done over the past few years.
Marvel Flair 2019 - Upperdeck
MNS Cards - Lon Chaney/ Art of Aragorn
Krampus Inked Nightmare 2019 - Attic Cards
Star Wars Rise of Skywalker 2019 - Topps Cards
Of course, the art of creating these sketch cards early on was difficult to get to a good quality particular in some of the Topps sets as you were reliant on drawing from specific reference photos and some times the paper stock wasn't very easy to use with markers or some art materials, but now I've mixed in coloured pencils and mixed media on my cards which seems to work out looking a lot better even though the scans really don't do the cards justice.
The best thing about working for other companies though is for every set amount of cards you have to draw for them you get some cards back called Artist Proofs which you can keep and sell at whatever price you want. This is often where you make back more money as you are selling an original one off sketch card were you could price it between £100 to £200 or even more depending on the demand for your art.
Other ways to make money drawing sketch cards are your own personal commissioned sketch cards, usually called PSC;s these can be made up of cards you have for this purpose which you commission on a contact basis through people that have seen and liked your work.
I've seen other Artists keep some Artist Proofs (AP's)back blank for this very purpose which makes sense as the customer can usually express what art they want on the cards.
One of the best tips I can give you about obtaining sketch card work is to keep active on social media, more often than not I've come across hidden gems of opportunities that wouldn't have happened had I not been a part of a facebook group or another Artists Instagram or Twitter page. Networking is key to getting these jobs.
The pay can fluctuate from as little as $3 per card to upwards of $5, $8 or $10 per card or more, but the more cards you are able to do potentially the more money you could make.
Drawing these cards won't make you rich, but it can be classed as one income stream you could add to many others that could benefit you in time and also it can open more doors for you as an Artist to gain commissions and more paid freelance art work.
Please, ask me anything in the comments about drawing sketch cards, I'd be happy to answer. Cheers!