Without any by-laws, you really have no framework to operate in. Essentially, there are no rules. Certainly you can be a monkey wrench in the groups efforts to get themselves certified with the umbrella organization, but at this point they seem to be nothing more than an informal group of people so unless they all agree to adhere to whatever set of rules you provide them, they are not required to do so.
If enough people in the group are of a like mind with yours, then you should have little trouble getting back on the board. But, lacking that I don't know that you have much more to go on besides the strength of personality and reason.
You would not be the first person who started an organization only to be ousted before it blossomed into its own. Sometimes it outgrows the conceptual idea of the original founder and that is unfortunate, but it happens. It sounds to me that this is less about some allegation of wrongdoing and more about a political power struggle within the group. As such, without by-laws, there is really nothing to fall back on as a guiding authority unless the group all agrees to adhere to whatever model by-laws the umbrella organization has for your organization. In other words, you will have to gain consensus - agreement - on the rules and then you will have to move within them to get the results you seek.
- Carl