It is really tough sometimes. I actually deal with supply chain issues daily in my day job; I take that knowledge to my business haha.
It is good to always have backups to your suppliers. I have a couple of higher-cost ones that I order from if my "preferred" supplier is backed up and can't service me in time. So my first backup is the same quality, higher pricing, similar turnaround. If I am really in a bind and need to service my customers, I will go to a supplier with the same quality with much higher pricing for faster turnaround. I really do have lists of suppliers for different things -- it's a nice little excel sheet. Not very complicated, but it's nice to have everything located in one place.
I would recommend evaluating alternate suppliers when you're not as busy as the holiday season. Find out who supplies what, at what price, and what their lead time is. You can ask for some samples of their products (let them know that you're interested in moving your business to them). Sometimes you will get it for free and sometimes you will get it at a low cost. From this, you can see their quality of product and you can get a glimpse of their customer service. If you're happy with it, order a full-sized order and see if you're happy with the results.
Where it gets tricky is OOAK sellers because you CAN'T find the supply anywhere else. This is where you need to order as far in advance as possible. This may mean a 3 month lead time or more! It's always a gamble ordering stuff in bulk, so also evaluate how you would destash your excess.
That's my two cents! Sure, it may seem like overkill, but it really helps minimize your risk in times like these. :)