Hi, I'm admittedly super new to Houdini, but something that keeps popping up on tutorials I see is something called a “Fluid Source”. I've read that this was phased out in version 17 and 18, but is there a workaround process that emulates this? Something to do with adding a pyrosource maybe?
I'm currently following a tutorial to make a simple shockwave as shown in the attachment, but would super appreciate any help on this.

Just use the new workflow from H17 forward. Don't waste your time with old tutorial versions. You can filter by version under the Tutorials menu at the top of this web page. It's under the Learn menu.