I'm pretty sure that ship does not exist within the Official Legends timeline.
Well in canon Clone wars some of those ships was not used by Republic or CIS but in canon CW CIS was not conquer Mandalor so they are not have access to mandalorian ships...
The reason they didn't have access to Mandalorian ships was because there were no mandalorian ships to access. All of the Mandalorian warship designs were well over 3,000 years old, thus making them extremely outdated compared to modern designs.
...similar with the Harrower if CIS win in Battle for Coruscant than Sith lord will give access to CIS for building Harrower...
The CIS wouldn't have been able to get Harrowers even if they wanted to. The CIS showed no interest in using ships that were over 3,000 years old.
...there are only two Subjugator ships in canon Malevolence and Devastation...
Actually, if you look at all of Legends there were at least 5 Subjugator-Class Heavy Cruisers that were used by the CIS (Subjugator, Malevolence, Devastation, Malevolence II, Unidentified).
but I think that would be nice to see both of those ships but it would be nice to see third version (this is not canon), if is dead Anakin S., Palpatin and Obi One and if CIS have access to Calamari Moon than General Grievous can build third version of subjugator and this ship will have only standard weapons (normal lasers and normal ion weapons) not some super weapon that would be Malevolence without those super ion weapon.
I can't speak for the team as I have no idea what they plan to do (neither do they at this point, if what Corey says regarding FotR is accurate) but I would assume the CIS would be able to build Subjugators like the IR can build Executors. The Subjugator
was one such cruiser without any of the super-weapons. It was instead armed with a Trihexalon Launcher, alongside the standard armament for a Subjugator-Class.
I want to say what if CIS conquer Mandalore or they win in Battle for Coruscant or Anakin and Obi-Wan was killed or they conquer Calamari Moon or what if Rendili is conquered in those cases CIS must have access to some new tehnology...
If the CIS were to gain control of any of those planets, they probably would have continued to produce their own units. They might make use of captured vessels, but they likely wouldn't produce more of them.
...same with Republic in beginning they should have one Invincible-Class Dreadnaught (with new weapon) and it is not buildable more of them but when CIS destroy this ship than Republic can build on Kuat Mandator MKI dreadnought after this ship is destroyed than can be build Mandator MKII dreadnought and if Republic lose Battle for Coruscant and if in battle was killed Anakin and Obi-Wan then Republic should have access to one legator star dreadnought.
The Republic did not have any Invincible-Class Dreadnaughts in their Navy at the time of the Clone Wars. Those ships were most likely decommissioned well before the beginning of the Stark Hyperspace War due to the Republic's decision to de-militarize. The Republic could build Mandators like the IR builds Executors in ICW, and Legators are not real ships.