[Suicide Junkie]

For planets, add some troops or UPCs; jubilant population gets a SY production bonus.
Use a multi-spaceyard allowing mod.

A second option is to multitask a ton of orbital factories.
By building 20 or 30 ships simultaneously, you can get your big fleet out faster.

And, thirdly, you can use retroseries.
Have your space yards build a stripped down Version of the warship hull in two or three turns. Then retrofit to a design that costs 45% more. Repeat until you have a vehicle that can be retrofitted to your desired warship design.
Note: you will spend more money on all those retrofits than you would have building them straight up, and will have to pay maintenance while the retrofits are installed. A pile of dedicated repair bases may be appropriate.