@Trigonometry
Just search for it on google. There are several of them out there. I've tried a few and they were all ok-ish. Expect for the conversion to be slow and with occasional failures. Most sites charge between $50 - $250 for the software, but it all works the same. I'm pretty sure they are all just slapping different UI's over the same library.
Here's one I've purchased and used:
http://3doc.i3dconverter.com/register.html /
http://3doc.i3dconverter.com/I've got a few of these converters ... the sites that sell them come and go. None of the sites even know what IMVU is ... they refer to XMF as the CAL3D format, which is the 3D engine that IMVU uses. Anything for converting and manipulating CAL3D files will also work on IMVU assets.
Keep in mind, the conversion normally only works on decompiled assets, so you do have to decompile the assets before converting them. You can buy CAL3D decompilers here:
buysell/black_market_index.php?mode=search&question=decompiler