Assalam-o-alikum my brothers and sisters in Islam.
I really feel sad as well as ashamed that this kind of thing happens in our community.
If this is of some consolence to you then allow me to state the reason I think is behind this behavior.
Most of the Muslims in the west are immigrants, and among them majority are first generation immigrants. The first generation immigrants have to do a lot of struggle. First they have to establish themselves, they don't have anyone to fall to if something happens to them so they work hard to make a living, plus they also have to learn the local language and culture etc which is quite difficult. So because of language and cultural issues they become shy of the local people. They also start missing their country and culture and food etc. and this leads them to seek refuge among the people of their own country/culture. That is why you will notice that Pakistanis stay with Pakistanis and Egyptians stay with Egyptians etc. I am not defending this wrong behavior but trying to explain it.
Also when these Muslims were living in their own country, they had Muslims living all around them so they never developed any habit of getting closer to strangers or even saying Salam to strangers, which is very bad according to Islam, but when everyone around you is a Muslim then it becomes hard to keep up with this tradition. And so they bring this thing here and do not say Salam to anyone they don't know. I think the second generation of Muslims will be different because they don't have any language and cultural issue and they don't care where you are from, so they will be able to integrate with reverts and all other Muslims more easily and thoroughly.
In the mean time we have this issue about which I have thought a lot, and I have come to a conclusion that this group of first generation immigrant will not change their behavior. I have no hope with them. They have built Mosques and established the basic infrastructure for the future generation but have done nothing to integrate the Muslim community. This will be the task of the next generation. But what should we do about the Muslims who converted to Islam and are now left alone to defend themselves against loneliness and frustration.
Since I have no hope that the current generation of Muslims immigrants will change their behavior, the reverts should take the matter in their own hands, take charge and do somethings to address this issue like:
1. Print this article and post it in the bulletin board of Mosques you go to. Maybe it will put some Muslims to shame and they start doing something to address this issue.
2. Arrange meeting (Halaqa) in your home on regular basis (e.g. on every Thursday evening or Sunday afternoon etc.) in which you invite people from your local Masjid. It may cost some money initially if you also provide some snacks like chips and coke etc. But it will help you in making yourself introduced to the community and get familiar with them too. Eventually people will know you and start inviting you to their homes too. Why this is important? because in a close community people go to each others homes, it promotes love and affection among people.
3. If you find reverts in your area then have a Halaqa (group meeting) of those reverts too on regular basis.
Brother and sisters human being is a social creature, you cannot live alone for a long time. I know it is hard to mingle among people who feel no desire to mingle, but you have to do it. I would do it if I am in your situation. May be not all be friendly, but some will definetly respond. You can see where I live and if there is any brother or sister live around here then send me a PM, Me and/or my wife will be happy to do whatever we could to help.