Have you tried using the SvnClient class? There's a couple of options you have with that:
Firstly: How to get latest revision number from SharpSVN?
or this:
using (SvnClient client = new SvnClient())
{
Collection<SvnLogEventArgs> logEventArgs;
SvnLogArgs logArgs = new SvnLogArgs
{
Limit = 1
};
client.GetLog(target, logArgs, out logEventArgs);
DateTime revisionTime = logEventArgs[0].Time;
}