Intercessor Gunner with Auxiliary Grenade Launcher

Hello, new to The Hobby here. I have a team of Angels of Death but I'm missing an Intercessor Gunner. Where is a good place to get a kit bashable unit or even just the weapon itself? I want to avoid buying the entire Intercessor box just for 1 guy but so far unsure of where else to find it.

I am kitbashing my primaris bois into Salamanders. Vulkan Lives!

Thanks!