... DXF group 34 or obj.measurement ...
Actually it is DXF 42 for dimensions
Alright, try this....
(defun C:dimsel()
(setq searchdist (getdist "\nEnter length dimension to find: "))
(setq a (entget (car (entsel))))
(if (= (distof(rtos searchdist (getvar "lunits")(getvar "luprec")))
(distof(rtos (cdr (assoc 42 a))(getvar "lunits")(getvar "luprec"))))
(progn
(redraw (cdr (assoc -1 a)) 3)
(princ "\n/Match found")
)
)
)
Now what this will do is find a single dimension that you select and test it against the entered dimension length for finding. Of course the dimension will match if you type in the length of the dimension you are going to select. It should be a simple thing to make the routine filter the selected dimensions and test them against the default searchdist.
In order to make sure the dimensions are equal, rather than use a fuzz factor, I simply had both numbers converted to the same string format using the same rounding, then converted to a number using the same rounding. This way when the dimension is set to 1/8" accuracy, and the dimension is actually at 3/32, it will find it as a match if you enter 1/8"
I have not done extensive testing, but I am sure with the many talented people here, we will see some more code to improve upon this rudimentary incarnation.
The routine will highlight the dimension if it is found to match the entered value.
Let us know if this is the direction you want to go...