Hey boys and girls, ever seen a model on the GMOD workshop that you thought "hot damn, I could really use that in SFM, but these bloody workshop models are in .gma format. I don't know what to do with this piece of junk!" Well look no further, I'm going to tell you how to do it!
I found this tool on facepunch a while back, very simple to use. It's a GMA Converter. What it does is extracts the files out of the .gma file in question, and creates a folder of the addon in your addons folder, where you can find the necessary folders (materials and models) for addition into SFM.
First you'll need the converter itself. I'm too lazy to find it again on facepunch, so I'm just gonna upload the one I've got.
Click Here to download the Converter!
Now, open that zip and extract its contents into a folder, name it whatever you want, just so long as you can easily find it again if you need to do this again. I just named mine GMA Converter. Easy enough.
Now start it up, it should look like this:
Now click on Convert A Single File. This will open a dialog where you can see your GMOD addons folder, and if it's not there then point it to it. Here you can scroll down to find all your workshop addons; the .gma files.
Now select the file you wish to convert. As an example, let's say I need a nice looking cigarette model for a pose. I'm gonna select the Shibboro Cigarettes .gma and convert it.
Press Open, and in less time than you can say "damn I love this new DigitalEro background", it's done!
Now open up your GMOD addons folder (if you haven't done so already) and find the folder it extracted to. It should be something pretty similar to what the .gma file was called. In this case, it is called Shibboro Cigarettes.
Now all you need to do is take the materials and models folders in there, and install them into SFM like any other model you would install, and presto! That's how you install GMOD workshop models into SFM!
And lastly, for proof it works: