First of all, you can download Gimp from here and then download the UFRaw installer from here. Well, after a few tries, I found out it is very tricky to make UFRaw work. Therefore I needed to install the UFRaw manually. I have downloaded and installed Gimp from here on my Windows 7 and 8 machines and unfortunately the installation package doesn't come with UFRaw. I found it was much easier for me to start with Gimp. It comes with many useful add-ons including UFRaw plug-in. However, if you download this package from here which is built by Simone Karin Lehmann, then your life will be much easier. So I would not recommend you to download and install both packages. Just so you know this version of Gimp must be run in X11.Well, I have tried to install Gimp via MacPorts but the UFRaw plug-in didn't work for me and to be honest I don't like the GUI with X11.
On the other hand, if you are familiar with MacPorts and you can just type the command in terminal " sudo port install gimp" and MacPorts will install all related packages for you including UFRaw. Since it doesn't have any add-ons in the package, then you have to manually install them by yourself, in this case, UFRaw plug-in.
If you download the dmg file from here (v2.8.2) which comes without any add-ons then you are in troubles. The 2.8.2 version GIMP runs on OSX natively. Well, after googling few hours and I found out some tips and tricks on how to install UFRaw plug-in to Gimp. Recently, I had problems to install UFRaw plug-in for Gimp on both of my Windows 7, 8 and my Macbook Pro (Mountain Lion).