Grammatically yes, but it's not a common way of speaking. We would say: There weren't many people. Or: There weren't enough people. (N.B. these mean different things --- a thousand people might not be enough.)

In most contexts, it's better to use "there was a lack of..." with uncountables: - there was a lack of colour in the garden - there was a lack of enthusiasm in the audience - there was a lack of salt in the food But as Matt says, you could just say something like, "there wasn't much..." 'lack' is more appropriate for slightly more formal contexts, or to add emphasis...