Do you have the dimensions that you are looking for? Posting a picture might help. Here are a few switch boots in different dimensions which could possibly be modified to fit your needs.
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These are from McMaster Carr and can be purchased in single units.
Covers for Toggle Switches
Protect toggle switches from moisture and dust by replacing your panel mounting nuts with these rubber covers.
Size For Max.
Toggle Dia. Overall Ht. Material Includes Specifications Met Choose a Color Each
1/4"-40 0.06" 0.5" Silicone Rubber Mounting Nut UL Recognized, C-UL Recognized Black, Gray, Red, White 70205K2 $5.68
1/4"-40 0.06" 0.59" Silicone Rubber Mounting Nut UL Recognized, C-UL Recognized Black, Gray, Red, White 70205K3 5.68
15/32"-32 0.22" 0.94" Silicone Rubber Mounting Nut UL Recognized, C-UL Recognized Black, Gray, Red, White 70205K4 4.20
15/32"-32 0.22" 1.09" Silicone Rubber Mounting Nut UL Recognized, C-UL Recognized Black, Gray 70205K75 5.28
15/32"-32 0.3" 1.11" Silicone Rubber Mounting Nut UL Recognized, C-UL Recognized Black, Gray 70205K29 7.53
1/2"-32 0.22" 0.84" Silicone Rubber Mounting Nut UL Recognized, C-UL Recognized Black, Gray 70205K77 4.92
M12 0.23" 0.86" Silicone Rubber Mounting Nut UL Recognized, C-UL Recognized Black 70205K26 5.28
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Grainger:
For Use With: IP66/68 Rated Pushbutton-Actuated Switches
Push Button Boot 3/16" 5/16" - 3/8" APM HEXSEAL 1UDL2 $3.85 / each
Push Button Boot 3/16" 5/16" - 3/8" APM HEXSEAL 1UDL3 $3.85 / each
Push Button Boot 27/64" 35/64" - 5/8" APM HEXSEAL 1UDL1 $3.50 / each
Push Button Boot 33/64" 39/64" - 3/4" APM HEXSEAL 1UDK9 $3.40 / each
For Use With: Marine, Industrial Controls, Power Tools, Chemical Food Processing Equipment, Communications, Test Equipment, Commercial and Consumer Appliances, Instrument Panels
Armored Toggle Switch Boot 7/32" 7/8" 5/8" 2-1/4" APM HEXSEAL 1UDJ2 $7.55 / each
Push Button Boot 27/64" 35/64" - 5/8" APM HEXSEAL 1UDK6 $3.50 / each
Push Button Boot 27/64" 35/64" - 5/8" APM HEXSEAL 1UDK5 $3.15 / each
Push Button Boot 27/64" 23/32" - 5/8" APM HEXSEAL 1UDK8 $3.50 / each
Push Button Boot 27/64" 23/32" - 5/8" APM HEXSEAL 1UDK7 $3.15 / each
For Use With: Mfr. No. MH11
Push Button Boot - - - - HUBBELL WIRING DEVICE-KELLEMS 3HZ98 $12.40 / each
Buying one of these boots and modifying it might be infinitely less expensive than having one produced.