not knowing what you've been looking at, (or what you actually need) I would like to see if the slot could be lengthened with a dremel. (depending on how much travel you really need).
IF you wanted to go the "modification" route.
will the bolts only be used for moderate privacy ? you know, just to keep the doors closed.
if it is for "security", you may have to go a different route.
if cosmetics is not an issue, you could make your own with a minimum of hand tools.

 

Thanks John, It's only needed for moderate privacy, e.g. to keep the doors closed and to keep the kids out of the bedroom at times.

Also if it's helpful, the Deltana f7bz10b is a typical example of the ones I was looking at.

 

Would you not plan for the base that screws to the floor and put a block of wood on the floor at least as high as the underlay.
Then after the carpet is in you locate the block and shave the carpet so the plate screws to the block?
I am not sure I have ever seen a lower bolt on an interior door.

 

Thanks Neal, I did plan to screw the base to the floor, but I hadn't thought of blocking it up to fill the gap. Awesome idea.

I am not sure I have ever seen a lower bolt on an interior door.

It will make the job easier if I simply omit the lower bolt,,, but I'm a little concerned that the doors would have a tendency to vibrate or rattle. Have you seen that in the past or is that concern unfounded?

 

yeah - that would be hard to modify.
in Florida, we have a lot of French Doors, mainly of glass panels, that had the same issues.
as a last resort, some have opted with either the pull down bolt that connects to the upper jam
or a barn door style bolt.
the bolts don't "have" to be on the bottom. you can put it at the top with a pull chain just as easy.

 

this is what I have - a Pull Down Chain Bolt.
but there are dozens of designs to choose from.

 

Imagine getting down to the kid's height and pushing on the door. The force is applied to the lower portion of the door and if it isn't secured, the doors will flex. Now think like a boisterous kid. If a little force got me that far, where will more force get me?

I recommend adding the lower flush bolt.