In GW's infinite wisdom, combi-weapons are hard (or impossible) to simply buy. You can get a single combi-melta and plasma in the "Space Marine Commander" box that GW sells for $20 ($17 on most online shops) or you can buy the single bits for $10/$5 respectively (pretty harsh if you want to include 6 combi-meltas...) The combi-flamer simply doesn't exist as a GW bit.
Besides the price issues, there's also the issue of their design. I'm just not a fan. To me, a one-use weapon should have the one-use part bellow the main weapon. I'm pretty much thinking of the how the M203 grenade launcher clips onto an M16:
To me, this just makes since, the main weapon is dominant on top, while the one shot part is under-slung. GW, however, has mixed feelings on this design note:
Don't ask me how that magazine reaches the chamber on the combi-plasma (right).
So now that we're clear on why I decided to make my own combi's, let's get onto the how. Thanks to the old-school Space-Wolf sprue, I was sitting on plenty of plastic meltas, so it made sense to start there
I started by dissecting the plastic melta into it's components: barrel, foregrip, and tank. I also made sure to preserve the cable - you never know when you might need something like this. I did the same to the bolter, removing the fore grip and barrel.
Mr. Bolter, meet Mr. Melta
This is by far the trickiest and most time consuming step, as you've got to be careful not to damage (or lose) any of the parts you're trying to harvest. After this it's just putting things back together:
I decided to go with a more "wolfy" bolter.
I also cut the foregrip down a bit to be flush with the bolter and rounded the edge of it off with a file. Next up were the barrels:
Note that the bolter barrel now actually lines up with the chamber... go figure.
And voila! There you have it. Once you get used to dissecting stuff with an exacto, it doesn't take too much to throw these together. I've also applied this method to combi plasmas and flamers. Here are the finished products of each type as wielded by my Deathwatch kill team:
Hey, this guy looks familiar...
Plasma pistols are perfect to use in this method.
Combi-flamer with stormbolter style magazine.