Besides BHIC there are 2 websites you could contact:
http://www.stadsarchief.nl
The city of ’s-Hertogenbosch has a website for genealogy research. Since both Carolus and Joanna were born there, their marriage could be listed in one of the parishes. Gerardus van Helmond, Joanna’s brother, born 1766 was baptized in St. Jacob church.
http://www.rhc-eindhoven.nl
The couple lived in Eindhoven, at the address Grote Berg 391 shown in “Bevolkingsregister”
Persoon Carel Smits
Plaats Eindhoven
Religie Rk
Beroep Spoel(d)er
Periode 1829 - 1829
Geboorteplaats 's Hertogenbosch
Leeftijd 73
Burgerlijke staat gehuwd
Bevolkingsregister Eindhoven inv. nr. 3 folio 121 volgnr. 5
Note that Carolus also was known as Smitjens:
Overledene Maria Smitjens
09-04-1803
Vader Carolus Smitjens
Moeder: Johanna Maria van Helmont
DTB Eindhoven inv.nr. 14.19 , folio 117
Hopefully someone is able to help.
Regards,