It sounds like you are asking for common property to be changed (which would require a special resolution) or even if the gate is your own lot property, you need the approval of the strata corporation.
However, if you feel they have been unreasonable in not even considering this you can apply for mediation through a private mediation service (there is no equivalent of Fair Trading in South Australia) or even take the strata scheme to the Magistrates Court for a ruling.
Here’s what the SA government’s publication Strata Titles – A Legal Guide says about unresolved disputes (and you can download it on that link):
If no resolution can be worked out, then an application may be made to the Magistrates Court as a minor civil action to decide the matter. If the matter is particularly complex or significant , a unit owner can seek the permission of the District Court to commence proceedings there [s41A(3)].
Alternatively, the District Court can agree to transfer proceedings begun in the Magistrates Court to the District Court .
An application can be made to the court by :
• a strata corporation
• the owner or occupier of a unit (including a tenant)
• a person who has contracted to purchase a unit
• any other person bound by the articles of a strata corporation except for persons invited to or visiting the site.
The court can deal with disputes where (1):
• it is claimed a breach of the Act or the articles of the corporation has occurred
• an occupier of a unit claims to have been prejudiced by the wrongful act or default of the strata corporation, or a delegate (including a strata manager), or the management committee, or some other member of the strata corporation
• a member of a strata corporation claims that a decision of the strata corporation, or a delegate (including a strata manager), or the management committee is unreasonable, oppressive or unjust
• any aspect of the occupation or use of a strata unit is in dispute between a strata corporation and a member of the corporation, or between two or more members of a strata corporation.
Obviously, it would be better to resolve these issues amicably, possibly via mediation. But, if that fails, you do have recourse to legal action if need be.
Oh, and there is no limit to the number of proxies that can be held by one person, provided they are given in the prescribed format (see the SA strata guide) and are available at the meeting for inspection. If they aren’t, your AGM may have been inquorate and another one should be arranged, as per the law.