Yes, you still need to file an extension. Here's the site for IRS. https://irsextension.online/?utm_source=bing&utm_medium=search&utm_campaign=[social security number ...
Your other option is to go ahead and file with the information you have and then file an amended return to add the additional information for a bigger refund.
One thing, if you think you owe, you need to send the amount you think you owe in with the extension.
