You could very well do so yourself.
It may seem cruel, but I am very much a "teach a man to fish" type, rather than the "give a man a fish" type. I want to make sure that you have "fish" for the years to come, rather than satisfying your immediate "hunger" (gee...I hope that's not too metaphorical

).
All the themes on the theme site are user submitted, every theme you see there involved someone thinking "I want this...", learning to do so, and then doing so.
I understand that some people will look at Rockbox and think that any work done thereon needs years of education and masses of degrees, but for the theme engine, this really isn't the case.
In fact, knowledge of any existing programming language won't help you at all here (well...it is /kinda/ LUA-ish in some respects, slightly...but I digress) - except possibly to help with the understanding of code flow and structure - the language used for the themes is unique to Rockbox.
Theme files (.fms, .sbs, .wps, etc.) in Rockbox are nothing more than simple plain text files read by the skin parser in core in the same fashion an English speaker would do so. Top to bottom, left to right. Contained therein are a series of "tags" and identifiers that tell the skin engine how you want it to behave. You can find this outlined in
the manual for your device, most of the tags have examples of usage also.
If you were to open your desired theme's files in <text_editor_of_your_choosing> and compare the tags therein with the manual, you should be able to get a grasp of exactly what is happening, and then make the changes to suit your liking (both of which are very trivial changes, by the way).
I will certainly be here to help if you get stuck, or have any questions, but I won't do this for you (nor should anyone else, in my opinion) as I think this is a great opportunity to not only learn something, but come out the end of it with a sense of achievement - and possibly a desire to go further with your new found knowledge.
[Saint]