In general, this information is quite valuable and (for casual games in particular) difficult to extract via data mining. Unfortunately this means you will likely have to pay for it if you want any kind of real details.
The Casual Gaming Association has some market research available for purchase. The Park Associates group does game market research (example study available here). Here is a collection of video game market reports, some of which may be relevant.
The NPD group is one such market research firm that provides some of their data to the public for free (but they still sell a fair bit of it). This wiki has a nicely categorized collection of their sales figures for example (since the NPD site itself can be a chore to navigate for real data). But the freely-available stuff is likely not going to be as well-separated as you want, so you probably can't extract much in the way of data to answer your questions about casual games. The NPD group also focuses mainly on retail distribution, which will exclude most casual games entirely.
Casual games present a particularly difficult challenge for market analysts and researchers because many such games exist in proprietary channels that are difficult to do data mining on, especially in a homogenous fashion (Steam is different than Facebook is different than some Flash web portal; everybody may use slightly different payment processors; sales of some casual games go to individuals and not neccessarily companies, so access to information on those apparently-interpersonal transactions may be more restricted; et cetera).
You can try your luck searching for "casual game market research" or "casual game market share." If all you really want is a rough high-level breakdown, perusing some of the articles from the latter query may give you what you need.