Hello,

You can try chlorosulfonic acid with future addition of Na2S. 

Dear Piyush

In the example one of the patent title: Process for manufacture of in vivo stain composition US 20010007904 A1 (link below) describe an industrial procedure to synthesize the thiosulfonic acid with the CAS number 43035-11-6 that you required. But, if you need it to produce methylene blue, you can synthesize the last one in a single step following the procedure described in the papten title: Process for preparing methylene blue US 4212971 A (link below)

for CAS: 43035-11-6

https://www.google.com/patents/US20010007904

for methylene blue

https://www.google.com/patents/US4212971