make your own.....here is how I would try it with the circuit board image , have done it similar with cut vinyl image
Start with an image like the one here obtained from the hundreds of photo sources on line . This one came from istock photo
Macro shot of the back side of a circuit board. Concept background.
www.istockphoto.com
get some water slide decale paper like this stuff here
https://www.amazon.com/dp/B077TMFVL9?psc=1&ref=ppx_yo2ov_dt_b_product_details
Resize the photo as you desire in any of the simple on line or microsoft photo image personally I like free download Faststone
https://www.faststone.org
Spiff up the image with Faststone color , size etc. If you do not have a high quality inkjet then take your waterslide paper to Staples and let them print it for you.
Add the decale you printed to your pen tube and cast it in resin, I like Aluminite and you have it.
I have not done this with the water slide decales yet but I have done it with cut vinyl transfer the picture here is a police pen made with the cut vinyl method. The water slide decal would be no different and actually better as you can have unlimited colors from a printer.
There are youtube vids on using waterslide decales for pen tubes.
There are youtube vids on using waterslide decales for pen tubes.
calabrese55