Thanks @Green_Eyed_Girl and welcome to the forum @ShyVixen 
grabs a tape measure the rim of the large head (on my Pro40) is about 2.5cm wide x 2.7cm long.
The large ones @Green_Eyed_Girl linked to I also have on my Premium and the rim is about 2.3cm wide x 2.5cm long.
Sadly they don’t fit on the pro40 because the depths are very different 
(1.6cm on the Premium heads to 2.3cm on the Pro40 heads).
I don’t have any of the medium ones to compare with I’m afraid!
If you think the sizing might work for you, you could maybe see if the manufacturer can supply some if you can’t get them from LH?