Try Silhouette Patterns, they have both thier machine and serger one on sale this month. The company is great to work with and very fast with their orders. the one they have for sewing machines is 18x24

I have the same machine and I bought my insert from the dealer. It was actually a table with removable legs. Pricey but a perfect fit and worth it. Last year I ordered a sewing table from Leah Day that also had an insert. My Viking insert however is the perfect fit without the legs and that is what I use. Leah Day insert still covered in paper. I wish machine manufacturers would include the insert or table top with the machines. Years ago I bought a cheap singer from Walmart and it came with the table. I mean who can sew without them these days. Makes all sewing so much easier. Good luck.

Just wanted to say thank you to Quiltingsunshine for the help getting me a table insert . Fits perfect thanks Annette