... bayou classic .... The kettle did not come with the stainless basket strainer. I'd like to purchase one for biab however cannot find one online sold separately...
Seems clear that what's desired here is to separately purchase the basket that would have originally came with the kettle.
My advice is to try BIAB with only the kettle and a bag.
You don't need the basket to protect the bag from heat. There should never be a need to apply heat while the bag is in the kettle. Except in extreme cold conditions, mash temps are easily maintained by putting some insulation (blanket, sleeping bag, etc.) over the kettle during the mash.
You don't need the basket for handling the bag. BIAB bags are easy to lift, especially if you can rig a hoist point overhead and lift the bag with a rope & pulley (letting gravity fully drain the bag into the kettle during the entire boil).
There are at least a couple of downsides to using a bag within a basket. It will separate a significant portion of your water from your grains during the mash. There's no benefit to that, and the basket will be just another piece that needs to be cleaned up at the end of the day.
Unless you have some specific need for the basket, don't buy it. Use your money for ingredients or something else.