Where can I find more themes for getsimple?

[Connie]

Because the platform templates joomla, drupal and other CMS are not compatible?

yes, each application has it's own way to merge content with themes
each system has it's own way of adding functionality to the themes

so you cannot use these themes with another system, no drupal theme with WordPress and no Typo3-theme with GetSimple

GetSimple is a dwarf compared with WordPress for example and that's why it seems not to be too interesting for theme designers, commercially I mean

but as GetSimple-template tags are easy to merge with HTML templates, (it's all in the WIKI), you can look for any "not-system-specific", plain HTML- or XML-template and adapt that to GetSimple

if you run into problems, I am sure the forum here will help you