As was said most parts can be fabbed.
You can post for parts here or ask the maker or HLJ for replacement ones.
Another option is how visible is the part and if the kit can live without it. Often a missing part can be hidden by doing some visible damage to the kit.
I work in a wood floored area so no carpet monster, many modelers put a vinyl sheet under the desk/chair to catch parts. Some also use a Jewellers apron.
Many of the kits I work with have small/fiddly parts, so parts are only removed when needed from sprue and go into a container(got a selection on my desk). If I can't finish the assembly, lid goes on the container and it goes into the box.
large chewing gum containers, metal boxes(snuffbox like) etc are great and cheap.
HTH.