They're harder to produce and not necessarily more interesting (or necessarily less) anyway. I do see that the British Library has parts for that string quartet op.246 (ca.1895) (not his first but possibly his only surviving? - Champlin/Apthorp (
Cyclopedia of Music and Musicians, volume 1, page 329, article written 1888 ("still living, 1888."), book published 1893) lists an earlier quartet, opus 93. Whether or not the works survive, first symphony in F was his opus 101, performed in 1873 or 1874; his 2nd in G minor, 1879, his opus 122. Also lists a polonaise for piano and orchestra, op.209, and other works. (Google downloadable-in-US pdf/EBook - may be at archive.org also.)
(Actually, see
IMSLP for the Cyclopedia. - should be on page 329 of volume 1 - not of the PDF but internal page 329. I forgot I'd uploaded that...)
Another list of his works up to about op.214 and 1881, with some dates of premieres (admittedly the orchestras in question have long since donated their holdings to the British Museum I expect) is in James Duff Brown's
Biographical dictionary of musicians: with a bibliography of English writings on music (1886) (pp165-6). (The first symphony was premiered at the Royal Albert Hall in August 1873, the 2nd symphony at the Promenade Concerts in August 1879 (that looks early- oh, ok, they started back in 1838?!!... ) It gives opus 93 as a -piano- quartet, not a string quartet, in E minor. (Looking at a google cache of Clarke's Wikipedia article there's a rather interesting Times review excerpted there of the 1st symphony's 1873 premiere suggesting that maybe I'm being too hasty above, and hope it might turn up
