I can't remember the exact figure off the top of my head, but it's something stupidly low like 100 tons an hour. Most people don't see the point of it. Quicker to grind the cash to buy it.
Laser mining in a decent miner will max out at about that, SD/SSD mining can get up to 200t an hour but even then that is slowed by time taken to unload and collect more ammo.
A full load in my Cutter 512 + 10t fitted with 2 x 2B SSDM doing a combination of both the above from carrier to carrier will take about 3.5 to 4 hours.
A high percentage of Icy rings have got Tritium hotspots and even those that have not will have a certain amount but it may be as low as 20t an hour to find.
And if I find a couple people who want to ride along, they might help mine some tritium.
This causes another set of problems, for long range carrier travel at max economy you need to keep the carrier as light as possible, the more weight the more Tritium used for each jump. dedicated passengers will need you to install extra facilities such as Shipyard and Outfitting, that's 4,750t of extra weight or less cargo space to carry extra Tritium plus an increase in fuel used each jump.
A single passenger in a single ship with no additional equipment weighs nothing, if they want to carry another ship you need a Shipyard fitted 3,000t, if they want to carry additional modules you would need Outfitting installed 1,750t. Plus an additional 11.5m cr per week running costs. - Passengers can be Expensive.
On the plus side any passenger owned ships or modules carried and any of your own ships and extra modules carried Do Not add to the weight of the carrier.
If you look at my carrier (link in sig) I am an out-black miner/explorer, I do not have Shipyard, Outfitting or Secure Warehouse fitted, (5,000t more cargo space). I mine my own Tritium as I go, I left Beagle Point with only the Tritium in my carrier tank, if I have any excess I will sell it in Colonia before heading back to the bubble to get rid of the rest of my cargo.