I usually try to order these forms as soon as they are available (towards the end of the year) so I can have them in hand by early January. Hint: Don't forget which tax year you are working on - one year I ordered the current year forms instead of the previous year and had to wait on another order to be mailed to check that task off my to-do list.
Follow this link for business forms (Information Returns and Employer Returns) such as 1099-MISC, 1099-NEC, 1096 (always order these with your 1099 forms!). Remember to order at least one set of instructions with each type of form.
Follow this link for personal and general forms.
P.S. I also keep extra stamps and envelopes on hand during tax season for use in these situations!