When I suggested that the OP could use a Weller TC201 soldering pencil on 24V DC instead of obtaing a 24V to 12V dc-dc converter, the question was raised as to whether the switch contacts in the TC201 would be subjected to excessive arcing when breaking the dc heater current.
After several emails trying to get my query to somebody in Cooper Tools who knew what they were talking about, I finally received an answer from a Production Engineer at Cooper Tools (Michael J. Naissen) which confirmed that there would be no adverse arcing or wear to the contacts when operating on 24V dc. The same switch unit is used on their 12V dc soldering tool where the heater carries double the current of the 24V dc TC201. Therefore the OP can safely use a TC201 directly on 24V dc instead of trying to find a suitable 12V converter.
The full text of the reply is as follows;
QUOTE: The SW60D switch is made by Weller in the USA. and is made for use only in Weller soldering tools. The specifications are for internal use only. If you propose a different use for the switch then please let me know and I will try to assist you. The SW60D is also used in the TCP 12, 12 volt tool which is specifically designed and rated for 12 volts DC and is supplied fitted with battery clips. At 12 volts DC the current switched is approximately double the current switched in a 24 volt tool. We do not have any trouble with early failure of switches in these tools. The specific answer to your original question is that we are quite happy to authorise and fully warrant the use of any TC201 or TC201B tool with a 24 volt DC power supply. In the event that the switch were to be used for any other purpose then no warranty would apply regardless of the voltage or whether AC or DC power was used. UNQUOTE: