MATLAB R2012b onwards the 32-bit version for Linux has been discontinued. You can download the R2012a release from this link:
https://in.mathworks.com/downloads/web_downloads/select_platform?dl_action=choose_products&tab=f
Note: you will not be able to access that page unless you have already associated a MATLAB license with your account. You will not be able to download from that page using a Trial version.