Recommendations for building unit cohesion in a reserve unit?

Building unit cohesion in the Reserves definitely has additional challenges. I would recommend three things:

1) Make sure to take full advantage of your AT period, whenever that comes. You can build a lot more cohesion by going through the tasks and challenges together in a period that is longer than a single weekend.

2) Bring this up to your squad leader, and ask to speak with the platoon sergeant if you think he will be responsive. It's likely that they don't know that this perception is happening, or they may not know that it is affecting other people as much as it is.

3) Volunteer for individual and especially group work details where you will be near the other members of the detail. Often the best time to get to know others is while working together on a task, instead of just trying to force it in between work. Ask the other Soldiers about themselves... let them do most of the talking and learn about their background. They should naturally open up to you.

Challenge your fellow Soldiers to be the best; the place that people want to serve and non-hackers are brought to standard.
Build a unit identity - a motto, unit t-shirts, something you are known for. Have a unit coin. A watering hole that your Soldiers go to celebrate a promotion, welcome new members, or salute a departing one.

Try to initiate some sort of unit function and take the lead on it. It can be as simple as lunch time bowling or a contest of who can make the best Dallas Cowboys joke.
Try to find something challenging. I've seen cohesion grow most when you guys go through things together.
Volunteering is another function I do a lot. Find your local Habitat for Humanity and get on the calendar to go help build a house. It's a lot of fun and you'll learn a thing or two.