One thing you could try if interested is raising your own catalpa seedlings to see if any slow-growing individuals appear. Growers have in the past tended to discard "runts" when choosing specimens to pot up or line out for growing on to sell. There is a tendency to try to produce as many crops as possible off of a site, thereby increasing income gained from it.

When a new dwarf cultivar is selected and reproduced it will be when the plant is thought distinctive and appealing enough to command the higher prices that will be wanted to cover the additional costs involved when a subject is slow-growing. Only some growers will be interested in undertaking such efforts.

So, a particular species may tend to give off many slow-growing seedlings yet have had few selections made from them. I don't know if catalpas are among this group or not.

Some kinds of trees also give off many variegated seedlings when raised from seed in a nursery situation, yet have not generated numbers of variegated cultivars. With variegated tree and shrub seedlings in general a common occurrence is for the variegated to become overcome and diminish or disappear as the specimen grows larger. What appear to be dwarf forms may also develop greater vigor with age.

OIKOS has an interesting hybrid dwarf catalpa -- link below:

Here is a link that might be useful: Dwarf catalpa

C. fargesii is a wild species from Asia and not a garden hybrid from Czechoslovakia. It produces pink flowers. A form I have seen here has been grown as C. fargesii f. duclouxii. One in Sumner, WA was 39' tall in 1993. Another, in Seattle measured 42' the previous year. Both were obtained by the same party from Hillier nursery in England.

The Oikos plant looks like C. ovata. One I have in a pot here I think may have been grown as 'Ecos' by the nursery I got it from. I have not seen flowers in person but Oikos photo resembles older C. ovata 'Flavescens' seen here, except for the flower color.

Thanks for the messages.
It's a bit confusing reading about that Cultivar.

Maybe there are dwarf forms of Catalpa ovata?

The fragrant path also has Catalpa x fargesii listed(which is where I got my source of seed).
"Unlike the American members of this tribe, this is a small Chinese Catalpa which may remain under ten feet and remarkably can bloom when only a foot or two tall and a couple years old. The pods are the typical length (about a foot) but are only pencil thin and often attract the attention of visitors. This and C. ovata would be good candidates for those who donÂt have room for the larger trees"

I kind of doubt that they are as dwarf as oikos or fragrant path says. In the 05-06 oikos catalog, their parent trees were 6-12 ft tall, but in the link that has been provided in this thread, the newest catalog says they are 10-20 ft now.
I have one that started from seed last year that is already 5+ tall and started flowering already. So the claim that they flower when young and late flowering rings true. My northern catalpa flowered around mid june, and this catalpa flowered a month and half later. I haven't had my chinese catalpa flower yet.

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There is no hybrid plant properly named Catalpa x fargesii. That name is taken by a pink-flowered Chinese species C. fargesii that had grown 42' tall by 1992 in a Seattle planting. Garbling/misapplication/transference of plant names like this is not unheard of in commerce. Nor is understatement of tree heights. It seems there is a fear of scaring people off with the truth about how tall trees may eventually grow on some sites.

Both the Oikos pictures and the ones immediately above appear to show the same plant producing leaves looking like those of C. ovata. The un-flowered seedling I have, probably from the same introduction is producing similar leaves to the pictures linked to/posted on this thread.

Plants distributed by Piroche Plants, Pitt Meadows BC as C. ovata have turned out to be C. ovata 'Flavescens' when seen later, in flower. The unusual coloring of this form makes it more distinctive and worthwhile than the white-flowered type shown here.

For a key (and links to descriptions) that can be used to check the leaf and flower characteristics of CC. fargesii, ovata against the plants being discussed on this thread...

Here is a link that might be useful: eFloras Flora of China - Catalpa