Although the max limit is 1000, you can use the limit and before options to fetch the previous bans, too. before is a snowflake, it tells Discord to consider only bans before this id.

So, if you have around 1200 bans, you can fetch the first 1000, grab the id of the last item in the returned collection and use its id as the before option in your second fetch:

let firstHalf = await guild.bans.fetch({ limit: 1000 });
let secondHalf = await guild.bans.fetch({ before: firstHalf.last().id, limit: 1000 });

You can also create a new function that fetches more than 1000 bans. There is an example below. This function returns a collection of GuildBans, so you can use the usual collection methods, like filter, each, etc.

async function fetchMoreBans(guild, limit = 2000) {
  if (!guild || typeof guild !== 'object')
    throw new Error(`Expected a guild, got "${typeof guild}"`);
  if (!Number.isInteger(limit))
    throw new Error(`Expected an integer, got ${typeof limit}.`);
  if (limit <= 1000) return guild.bans.fetch({ limit });

  let collection = new Collection();
  let lastId = null;
  let options = {};
  let remaining = limit;

  while (remaining > 0) {
    options.limit = remaining > 1000 ? 1000 : remaining;
    remaining = remaining > 1000 ? remaining - 1000 : 0;

    if (lastId) options.before = lastId;

    let bans = await guild.bans.fetch(options);

    if (!bans.last()) break;

    collection = collection.concat(bans);
    lastId = bans.last().id;
  }

  return collection;
}

Example usage:

client.on('messageCreate', async (message) => {
  if (message.author.bot) return;

  let banList = await fetchMore(message.guild, 1500);
  let filteredBanList = banList.filter(({ user }) =>
    user.username.toLowerCase().startsWith('e'),
  );

  console.log(`There are ${banList.size} bans fetched`);
  console.log(
    `Number of bans where the user's username starts with the letter "e": ${filteredBanList.size}`,
  );
});