Since SITC groups/subgroups are quite aggregate it is difficult to get data on price, let alone a time series. You may try indirectly by calculating unit values i.e. values normalized by quantity. But I am afraid you may not get quantity at that level of aggregation. In case you do, you may try this indirect albeit imperfect way of achieving what you want.

Thank you very much for your answers. Yes, I am working with Comtrade to calculate unit values and checking consistency with shorter time series I was able to find from UNCTAD and CEPII.