I'm afrain toasters are out of my field of expertise and I have never even personally seen the built-in toaster design you have except in pictures but here is what I do know about that product.

Modern Maid KBT-100 Built-in Toaster

Replacement parts for Modern Maid major appliances are handled by Amana. Modern Maid small appliances (like toasters) however where made by McGraw Edison's small appliance division which was purchased by Toastmaster whom is now owned by Salton.

You can try contacting Salton (see the link below) to see if they can supply replacement parts for your toaster. Failing that, if you can remove the unit I'm sure if you brought it to a local small appliance repair shop, they should be able to replace any broken elements or switches.

Modern Maid built-in toasters periodically come up for auction on eBay. There were two up for auction in 2003, two in 2004, one in April of 2006, three in 2007, two in Oct. 2008 (one new!), two in March 2009, one in February 2010, two in October 2011 (one new in box!), two in November 2011, one in July 2012 (NIB) and two in October 2013, one of them unused! More recently, there were 3 for auction in October 2015 ranging in price from $150 to $230, one in each of Jan. Feb and April 2016, one in Sept. 2017 and another in October 2017. Use the link below to see if any are currently for auction.

If nothing is currently up for auction on eBay and you're a registered eBay user (or don't mind registering with them which is FREE!), you can use the link to 'Follow this search' and eBay will email you whenever new items matching the search terms are auctioned! Just click the "Follow this search" or "Add to Favorite Searches" or "Save this search to Favorites" link on the search results page and follow the instructions.

Michael from Toaster Central in New York, NY said they have had good success in repairing these older units. See the link below for contact information to see if they can help with your unit.