There's also a web article that adds Dragonflesh, Stained Glass, & Brass 1/2 Golems from the MM2.
I believe The Underdark Adventure Guide also has Arcane Prosthetics.
And there's an eberron book which has construct grafts that are based on Warforged technology.
Finally, there's the 1/2...
A Half Golem is immune to ALL magic except the specified spells so yes, it would be immune to it's own spells except for any spells that are specified.
In a Half Iron Golems case, any fire, electricity or rust effect would still effect it, just like a full Iron Golem.
It wouldn't be up for...
Probably around +4. Their abilities seem OP at first until you realize that their magic immunity means they can never receive any form of magic healing, neither Cure spells nor potions.
And if they aren't constructs, then no repairs either. Meaning any damage that gets past their DR is just...
There are so many clockwork constructs in various books I'd be shock if there WASN'T a clockwork golem somewhere. However, the half golems, as far as I know, were only ever published covering the 4 original and the 3 from the MM2 which did not have a clockwork golem.
Keep in mind that Magic Immunity also means no magic healing. No potions, no friendly Cure spells. As an adventure progresses, your HP slowly depletes with no way to circumvent it. Afterward, you're taking weeks or months of downtime in full bed rest for ordinary healing. Not so overpowered...
I dont know which edition you're going for since I came here via link but the 3.5 Spell Compendium has this exact spell (lava instead of magma but it's the same thing) on p. 222 listed as a 9th level spell if that helps