Catchers aren't going to get you anything in return. People will just stick with what they have, as no catcher after the top 3-5 is worth trading for.
Bobby Crosby is someone people might want, as is Baldelli.
Just something to note, drafting 3 pitchers in the first 4 rounds is not a good idea. If you had only taken 2 SPs in the first 4 rounds, you could have nabbed a top notch 1B, which would have given you a very strong offense.
Trade one of your starters for an SP, and drop D Johnson and Lo Duca so you can pick up some pitching.
...Boston papers now and then suffer a sharp flurry of arithmetic on this score; indeed, for Williams to have distributed all his hits so they did nobody else any good would constitute a feat of placement unparalleled in the annals of selfishness. -Updike