Door lining for French door

You will not buy that size lining off the shelf it would need to be cut and routered out of two lining packs

You can get made to measure doors made. These are more expensive. But the size is the size. A decent joiner will be able to sort this for you.

You would need to buy two packs of standard door casings and use the leg from the second pack for the head.
Stores used to sell random lengths but I guess they got wise to selling another pack instead!
I would always ask at the timber yard if they had any damaged packs, and would they sell you one leg.

Personally I would make my own lining. You'll struggle to find that off the shelf.

I'd use inch thick PSE boards. Thickness of stud plus 30 mm to allow for plasterboard and a couple mm for skim.

When I fit door a lining to double doors like this, I will always make the lining up myself to suit out of finished timber. when you make the lining Remember to add 3mm for each gap in the door so 9mm in total. when the studs are built add the lining thickness plus the 9mm gap plus both door width and 10mm each side for packing. when fitting a lining for double doors its important the lining is in wined which means both legs are parallel to each other. this is the most important thing. also fit the doors before architrave as you can make adjustments to lining once door is hung. make sure the lining is fixed twice at least 400mm down each leg...... sorry there's a lot to it

also, when ripping the prepared timber to suit remember to allow 15mm for plaster board and plaster each side. so, if you have a 90mm stud wall, you will rip the prepared timber to 120mm. also plaster the walls before swing the doors as the moisture from plaster expands the doors....

i hope this helps

You would be looking for a French door or double doors internal door lining to suit the door set