Religious groups are typically comprised of communities of practitioners who visit the temple/church a couple of times a week and practice together. Is this true of secular Buddhism? If so, Where are the largest communities?
Secular Buddhism is expressing itself in ways beyond the imagination. There are people in the virtual world Second Life that are practicing Buddhism virtually. Secular Buddhist Association -- Supportive Virtual Buddhist Communities
There is talk of secular Buddhism all over the world. (search for communities of secular Buddhists)
What seems significant is that secular Buddhism is taking off. I would say that people hunger for the Buddhist experience and practice without the masks of religion that various sects require its monks to wear. This is not the end to Buddhism but a glorious new beginning that is sustainable in modern culture.
The largest group near you, depending on the size of the city (large metropolises usually have more specific options), will most likely be implicitly though a weekly meditation group. The experience of these groups, and the individuals in them, very widely. For other countries, it may be different.
How to actually find a meditation group near you? Well you're already online, why not start there? Then, paper bulletins of the group could be at the local public library, organic grocery store/shop, etc. Gold is only as good as the one digging.
Technically the SGI (Soka Gakkai International) is a lay Buddhist group, but there aren't any priests or nuns, so it may also be considered a secular form of Buddhism also. It is an orginization, but in my experience, I have never fealt like they were just trying to get my money or anything like that. There are many meetings that one can attend and there is a strong community emphasis, so you get to know a lot of people. Once a month, there is a big city-wide meeting which people often attend, but there is also a monthly district meeting, which usually comprises a small number of people (~5-20). In addition to that, there are many other meetings which one can attend (many do) outside of these two meetings. Usually at a meeting, there is a part where everyone medetates, and then after that, we often times talk and discuss the certain literary works of Nichiren Daishonin, a buddhist monk from the 1200's. That is where the meeting is more philosophical. After that, there may be food or something like that and people usually just talk with eachother. There are some meetings where there is only medetation (toso), and meetings where there is only philosophical discussion (study meetings). I'm not sure if that's what you're looking for, but that is probably one of the more common sects of Buddhism, so depending on that country you live in and the size of your city, there probably is at least a group of people there who practice. Here's a link to the SGI website if you're interested.