Most likely they'll have a few Points worth available for trade/sell on hand. The rest as needed, unless you wanted them as a group purchase. Like throwing them in as freebies when you order that Omni without the pods.
TT
Since I feel like doing the math, let's figure that out.
A few points = let's assume 2-3 Points' worth of rifles. Given how many people there are in a Clan Infantry Point, that works out to 50-75 rifles. Assume the local Sea Fox group only carries in Point-sized lots for logistical purposes, so it will be 50
or 75, with no in-between.
Average IS Foot Infantry Company is 3 Platoons. SLDF Standard is 4 7-man squads per Platoon for 28 soldiers, figure 84 soldiers in a Company, which means it wouldn't be enough. Adding a single support weapon to each squad, however, would lower the number to 72, which would leave you with three spares in the maximum case. Two support weapons in each squad would reduce your requirements to 60 rifles. You could still end up short if they're only carrying two Points worth.
IS Jump Infantry Platoon deletes a single squad for 21 men. A company would thus be 63 soldiers. A single support weapon per squad would leave your requirements at 54 rifles, which brings us within sight of the lower limit of the range. Go for two support weapons, and you only need 45 rifles, which would give you five spares
at the minimum (not recommended, since that reduces your jump capability).
Now, if they're carrying four Points' worth (100), or even enough for an entire Star (125), then the messing around with support weapons to ensure you have enough for every soldier who needs one would be pointless, but you'd have a comfortable reserve on hand to replace broken/lost rifles. If they only have enough for a single Point (25), then you could equip a Platoon with a single support weapon in each squad.