It sounds like you are looking for a plant with an above average number of leaves at maturity, at least in part ... this is not necessarily something that can be predicted from looking at very small plants. This is a variable species but it can be divided into two groups. In my reference (Monocotyledons) there are 2 subspecies: swobodae (including plants in the trade labeled as compacta) and the type (generally larger and solitary).
swobodae (70 to ~180 leaves)
vic-reg (as few as 150 but generally 280 to ~500 leaves)
I would imagine most of the plants for sale where you are would be the offsetting form, just based on the ease of propagation. The plant you like does appear to be compact and may break the general leaf count rule I have proposed, this would seem to relate to the extreme variability of the compact form.
The younger the plant, the more difficult it probably is to judge how many leaves it will have when mature. But if it is seed grown and not propagated from offsets, you have a higher chance of it being the larger, solitary, many-leafed form at maturity. That is of course unless the seed is collected from a compact plant. In any case, the seller may be able to provide clues in the form of a picture of the mother plant.
I hope this helps.
I don't know if size is an issue for you, more details here from the same reference:
swobodae: width 20-35cm
vic-reg: (20-)30-65cm
My experience with a total of 5 clones in containers, some not yet full size
swobodae: 23-28cm
vic-reg: 41-43cm
The smallest plant has the fewest leaves at maturity and the largest plant has the most leaves.
