The Small Seal script is not yet in Unicode. The script has a tentative allocation at U+30000..U+3291F in the Roadmap to the TIP for the Unicode Standard.
A number of proposals for its inclusion have been submitted to the Unicode Technical Committee and WG2:
2015-10-20 Proposal to encode Small Seal Script in UCS — TCA, China N.B. (WG2 N4688, L2/15-281)
2016-04-28 Proposal to Apply Source-Based Variation Selector in Shuowen Small Seal Encoding — Suzuki Toshiya (WG2 N4716, ( L2/16-092)
UTC #147 Minutes ( L2/16-121) (See B.16.1 for decision and action items)
2017-06-18 Shuowen Seal Encoding Design Issues — Suzuki Toshiya, Richard Cook (WG2 N4834, L2/17-250)
UTC #152 Minutes ( L2/17-222) (See C.21 for decision and action items)