The latest public SPICE Kernels for Solar Orbiter are available via the ESA SPICE Service here: https://www.cosmos.esa.int/web/spice/solar-orbiter
Solar Orbiter data are also available in the ESA WebGeocalc instance here: https://www.cosmos.esa.int/web/spice/webgeocalc
The contents of the SPICE kernels are described in SOL-SGS-TN-0017: SOC-Provided Ancillary Data For Solar Orbiter
Note that instrument teams will receive kernels via GFTS and should use those in the first instance. The content is the same but there may be a short delay before the latest kernels are made available via the SPICE Service.
Latest OBT->UTC SOC reference implementation:
SPICE homepage at NAIF/JPL: http://naif.jpl.nasa.gov/naif/
Solar Orbiter Home Page: https://www.cosmos.esa.int/web/solar-orbiter/